diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index ed89b7b..504eafe 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -12,7 +12,7 @@ on:
       - main
 
 jobs:
-  linting:
+  lint_and_pytest:
     runs-on: ubuntu-latest
     strategy:
       matrix:
@@ -47,12 +47,15 @@ jobs:
         flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
         # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
         flake8 . --count --exit-zero --max-complexity=10 --max-line-length=100 --statistics
+    - name: Pytest
+      run: |
+        pytest
     - name: Run linting environment and pre-commit hooks
       run: |
         tox -e lint
 
 
-  tox-coveralls:
+  coveralls:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
@@ -61,26 +64,12 @@ jobs:
         with:
           python-version: 3.7
 
-      - name: Set up Python 3.8
-        uses: actions/setup-python@v2
-        with:
-          python-version: 3.8
-
-      - name: Set up Python 3.9
-        uses: actions/setup-python@v2
-        with:
-          python-version: 3.9
-
       - name: Install python dependencies
         run: |
           python -m pip install --upgrade pip
           python -m pip install tox pytest pytest-cov coverage responses
           if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
 
-      - name: Tox testenv
-        run: |
-          tox
-
       - name: Pytest
         run: |
           pytest
@@ -92,7 +81,7 @@ jobs:
           flag-name: Python Test Suite
 
   coveralls_finish:
-    needs: tox-coveralls
+    needs: coveralls
     runs-on: ubuntu-latest
     steps:
       - name: Coveralls Finished
diff --git a/README.md b/README.md
index 699ecd4..016cc5e 100644
--- a/README.md
+++ b/README.md
@@ -76,37 +76,30 @@ on `osx / linux / bashonwindows`:
 curl -sSL https://raw.githubusercontent.com/python-poetry/poetry/master/get-poetry.py | python -
 ```
 
-- Once you have **Poetry** installed you need to install the projects dependencies with this command:
+- Once you have **Poetry** installed you need to install the projects dependencies with this command from the project root:
 
 ```bash
-poetry install
+bin/setup
 ```
+- This script will install all dependencies specified in `pyproject.toml` via `Poetry` and install the `pre-commit` hooks
+this project uses.
 
-- After you have installed **Poetry**, you need to start the python environment managed by Poetry by
-  running `poetry shell` in your terminal.
-
+## Adding dependencies to the project
+If your changes require you to install a python package/module using `poetry add <some package>` or
+`poetry add <some package> -D` for a dev dependency. You will also need to run the following command to
+regenerate a `requirements.txt` file that includes the newly added dependencies:
 ```bash
-poetry shell
- ```
+poetry export -f requirements.txt --output requirements.txt --without-hashes --dev
+```
 
-### Pre-Commit Hooks
+## Pre-Commit Hooks
 We are using [Pre-Commit](https://pre-commit.com/) to enforce formatting, lint rules, and code analysis so that
 this repo is always in good health.
- - If you choose not to globally install `pre-commit`, then you can skip installing via `pip` or `homebrew` directly.
-   You can simply run either `pip install -r requirements.txt` or `poetry install`
-To be able to push a PR to the repo after making changes locally, you will need to install `pre-commit` which
-is a tool that runs linting, formatting, and code analysis on your changes.
-```bash
-pip install pre-commit  # Install via pip
+- `Pre-Commit` is installed and initialized when you run `bin/setup` from the project root as outlined above.
 
-OR
-
-brew install pre-commit  # Install via homebrew
-```
-- After you have run either `pip install -r requirements.txt`, `poetry install`, or globally installed
-  [Pre-Commit](https://pre-commit.com/) using the above commands you need to run the following command
-  in the project directory locally. This allows the pre-commit hooks to run when you are looking to commit
-  and push code to this repository.
+- If you choose not to use `Poetry` and prefer `pip` you can simply run `pip install -r requirements.txt`
+To be able to commit & push a PR to the repo after making changes locally, you will need to install `pre-commit` which
+is a tool that runs tests, linting, formatting, and code analysis on your changes.
 ```bash
 pre-commit install
 ```
diff --git a/bin/setup b/bin/setup
new file mode 100755
index 0000000..1ef36e2
--- /dev/null
+++ b/bin/setup
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+poetry install
+pre-commit install
+poetry shell
diff --git a/poetry.lock b/poetry.lock
index 91ab14e..4e38846 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -74,6 +74,17 @@ python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
 [package.dependencies]
 pytz = ">=2015.7"
 
+[[package]]
+name = "base58"
+version = "2.1.0"
+description = "Base58 and Base58Check implementation."
+category = "main"
+optional = false
+python-versions = ">=3.5"
+
+[package.extras]
+tests = ["pytest (>=4.6)", "pytest-flake8", "pytest-cov", "PyHamcrest (>=2.0.2)", "coveralls", "pytest-benchmark"]
+
 [[package]]
 name = "black"
 version = "20.8b1"
@@ -208,6 +219,17 @@ category = "dev"
 optional = false
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*"
 
+[[package]]
+name = "execnet"
+version = "1.9.0"
+description = "execnet: rapid multi-Python deployment"
+category = "dev"
+optional = false
+python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*"
+
+[package.extras]
+testing = ["pre-commit"]
+
 [[package]]
 name = "filelock"
 version = "3.0.12"
@@ -230,6 +252,17 @@ mccabe = ">=0.6.0,<0.7.0"
 pycodestyle = ">=2.7.0,<2.8.0"
 pyflakes = ">=2.3.0,<2.4.0"
 
+[[package]]
+name = "fuuid"
+version = "0.1.0"
+description = "Functional UUIDs for Python."
+category = "main"
+optional = false
+python-versions = ">=3.7,<4.0"
+
+[package.dependencies]
+base58 = ">=2.1.0,<3.0.0"
+
 [[package]]
 name = "identify"
 version = "2.2.10"
@@ -259,7 +292,7 @@ python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
 
 [[package]]
 name = "importlib-metadata"
-version = "4.6.0"
+version = "4.6.1"
 description = "Read metadata from Python packages"
 category = "dev"
 optional = false
@@ -274,6 +307,14 @@ docs = ["sphinx", "jaraco.packaging (>=8.2)", "rst.linker (>=1.9)"]
 perf = ["ipython"]
 testing = ["pytest (>=4.6)", "pytest-checkdocs (>=2.4)", "pytest-flake8", "pytest-cov", "pytest-enabler (>=1.0.1)", "packaging", "pep517", "pyfakefs", "flufl.flake8", "pytest-perf (>=0.9.2)", "pytest-black (>=0.3.7)", "pytest-mypy", "importlib-resources (>=1.3)"]
 
+[[package]]
+name = "iniconfig"
+version = "1.1.1"
+description = "iniconfig: brain-dead simple config-ini parsing"
+category = "dev"
+optional = false
+python-versions = "*"
+
 [[package]]
 name = "isort"
 version = "5.9.1"
@@ -343,14 +384,6 @@ category = "dev"
 optional = false
 python-versions = "*"
 
-[[package]]
-name = "more-itertools"
-version = "8.8.0"
-description = "More routines for operating on iterables, beyond itertools"
-category = "dev"
-optional = false
-python-versions = ">=3.5"
-
 [[package]]
 name = "multidict"
 version = "5.1.0"
@@ -377,11 +410,11 @@ python-versions = "*"
 
 [[package]]
 name = "packaging"
-version = "20.9"
+version = "21.0"
 description = "Core utilities for Python packages"
 category = "dev"
 optional = false
-python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
+python-versions = ">=3.6"
 
 [package.dependencies]
 pyparsing = ">=2.0.2"
@@ -467,26 +500,37 @@ python-versions = ">=2.6, !=3.0.*, !=3.1.*, !=3.2.*"
 
 [[package]]
 name = "pytest"
-version = "4.6.11"
+version = "6.2.4"
 description = "pytest: simple powerful testing with Python"
 category = "dev"
 optional = false
-python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,>=2.7"
+python-versions = ">=3.6"
 
 [package.dependencies]
-atomicwrites = ">=1.0"
-attrs = ">=17.4.0"
-colorama = {version = "*", markers = "sys_platform == \"win32\" and python_version != \"3.4\""}
+atomicwrites = {version = ">=1.0", markers = "sys_platform == \"win32\""}
+attrs = ">=19.2.0"
+colorama = {version = "*", markers = "sys_platform == \"win32\""}
 importlib-metadata = {version = ">=0.12", markers = "python_version < \"3.8\""}
-more-itertools = {version = ">=4.0.0", markers = "python_version > \"2.7\""}
+iniconfig = "*"
 packaging = "*"
-pluggy = ">=0.12,<1.0"
-py = ">=1.5.0"
-six = ">=1.10.0"
-wcwidth = "*"
+pluggy = ">=0.12,<1.0.0a1"
+py = ">=1.8.2"
+toml = "*"
 
 [package.extras]
-testing = ["argcomplete", "hypothesis (>=3.56)", "nose", "requests", "mock"]
+testing = ["argcomplete", "hypothesis (>=3.56)", "mock", "nose", "requests", "xmlschema"]
+
+[[package]]
+name = "pytest-cache"
+version = "1.0"
+description = "pytest plugin with mechanisms for caching across test runs"
+category = "dev"
+optional = false
+python-versions = "*"
+
+[package.dependencies]
+execnet = ">=1.1.dev1"
+pytest = ">=2.2"
 
 [[package]]
 name = "pytest-cov"
@@ -504,6 +548,34 @@ toml = "*"
 [package.extras]
 testing = ["fields", "hunter", "process-tests", "six", "pytest-xdist", "virtualenv"]
 
+[[package]]
+name = "pytest-mock"
+version = "3.6.1"
+description = "Thin-wrapper around the mock package for easier use with pytest"
+category = "dev"
+optional = false
+python-versions = ">=3.6"
+
+[package.dependencies]
+pytest = ">=5.0"
+
+[package.extras]
+dev = ["pre-commit", "tox", "pytest-asyncio"]
+
+[[package]]
+name = "pytest-watch"
+version = "4.2.0"
+description = "Local continuous test runner with pytest and watchdog."
+category = "dev"
+optional = false
+python-versions = "*"
+
+[package.dependencies]
+colorama = ">=0.3.3"
+docopt = ">=0.4.0"
+pytest = ">=2.6.4"
+watchdog = ">=0.6.0"
+
 [[package]]
 name = "python-dotenv"
 version = "0.15.0"
@@ -533,7 +605,7 @@ python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*, !=3.5.*"
 
 [[package]]
 name = "regex"
-version = "2021.4.4"
+version = "2021.7.6"
 description = "Alternative regular expression module, to replace re."
 category = "dev"
 optional = false
@@ -791,12 +863,15 @@ docs = ["proselint (>=0.10.2)", "sphinx (>=3)", "sphinx-argparse (>=0.2.5)", "sp
 testing = ["coverage (>=4)", "coverage-enable-subprocess (>=1)", "flaky (>=3)", "pytest (>=4)", "pytest-env (>=0.6.2)", "pytest-freezegun (>=0.4.1)", "pytest-mock (>=2)", "pytest-randomly (>=1)", "pytest-timeout (>=1)", "packaging (>=20.0)", "xonsh (>=0.9.16)"]
 
 [[package]]
-name = "wcwidth"
-version = "0.2.5"
-description = "Measures the displayed width of unicode strings in a terminal"
+name = "watchdog"
+version = "2.1.3"
+description = "Filesystem events monitoring"
 category = "dev"
 optional = false
-python-versions = "*"
+python-versions = ">=3.6"
+
+[package.extras]
+watchmedo = ["PyYAML (>=3.10)", "argh (>=0.24.1)"]
 
 [[package]]
 name = "yarl"
@@ -813,7 +888,7 @@ typing-extensions = {version = ">=3.7.4", markers = "python_version < \"3.8\""}
 
 [[package]]
 name = "zipp"
-version = "3.4.1"
+version = "3.5.0"
 description = "Backport of pathlib-compatible object wrapper for zip files"
 category = "dev"
 optional = false
@@ -821,12 +896,12 @@ python-versions = ">=3.6"
 
 [package.extras]
 docs = ["sphinx", "jaraco.packaging (>=8.2)", "rst.linker (>=1.9)"]
-testing = ["pytest (>=4.6)", "pytest-checkdocs (>=1.2.3)", "pytest-flake8", "pytest-cov", "pytest-enabler", "jaraco.itertools", "func-timeout", "pytest-black (>=0.3.7)", "pytest-mypy"]
+testing = ["pytest (>=4.6)", "pytest-checkdocs (>=2.4)", "pytest-flake8", "pytest-cov", "pytest-enabler (>=1.0.1)", "jaraco.itertools", "func-timeout", "pytest-black (>=0.3.7)", "pytest-mypy"]
 
 [metadata]
 lock-version = "1.1"
 python-versions = "^3.7"
-content-hash = "2f4c29be3ad34cf982b28e4a892b6289c196d5d7c492b287afe67abaa68df6d1"
+content-hash = "44a12436d6071b62002beab90bd98605720f47f4c08c492d52f1b482efaeadbf"
 
 [metadata.files]
 aiohttp = [
@@ -892,6 +967,10 @@ babel = [
     {file = "Babel-2.9.1-py2.py3-none-any.whl", hash = "sha256:ab49e12b91d937cd11f0b67cb259a57ab4ad2b59ac7a3b41d6c06c0ac5b0def9"},
     {file = "Babel-2.9.1.tar.gz", hash = "sha256:bc0c176f9f6a994582230df350aa6e05ba2ebe4b3ac317eab29d9be5d2768da0"},
 ]
+base58 = [
+    {file = "base58-2.1.0-py3-none-any.whl", hash = "sha256:8225891d501b68c843ffe30b86371f844a21c6ba00da76f52f9b998ba771fb48"},
+    {file = "base58-2.1.0.tar.gz", hash = "sha256:171a547b4a3c61e1ae3807224a6f7aec75e364c4395e7562649d7335768001a2"},
+]
 black = [
     {file = "black-20.8b1.tar.gz", hash = "sha256:1c02557aa099101b9d21496f8a914e9ed2222ef70336404eeeac8edba836fbea"},
 ]
@@ -988,6 +1067,10 @@ docutils = [
     {file = "docutils-0.16-py2.py3-none-any.whl", hash = "sha256:0c5b78adfbf7762415433f5515cd5c9e762339e23369dbe8000d84a4bf4ab3af"},
     {file = "docutils-0.16.tar.gz", hash = "sha256:c2de3a60e9e7d07be26b7f2b00ca0309c207e06c100f9cc2a94931fc75a478fc"},
 ]
+execnet = [
+    {file = "execnet-1.9.0-py2.py3-none-any.whl", hash = "sha256:a295f7cc774947aac58dde7fdc85f4aa00c42adf5d8f5468fc630c1acf30a142"},
+    {file = "execnet-1.9.0.tar.gz", hash = "sha256:8f694f3ba9cc92cab508b152dcfe322153975c29bda272e2fd7f3f00f36e47c5"},
+]
 filelock = [
     {file = "filelock-3.0.12-py3-none-any.whl", hash = "sha256:929b7d63ec5b7d6b71b0fa5ac14e030b3f70b75747cef1b10da9b879fef15836"},
     {file = "filelock-3.0.12.tar.gz", hash = "sha256:18d82244ee114f543149c66a6e0c14e9c4f8a1044b5cdaadd0f82159d6a6ff59"},
@@ -996,6 +1079,9 @@ flake8 = [
     {file = "flake8-3.9.2-py2.py3-none-any.whl", hash = "sha256:bf8fd333346d844f616e8d47905ef3a3384edae6b4e9beb0c5101e25e3110907"},
     {file = "flake8-3.9.2.tar.gz", hash = "sha256:07528381786f2a6237b061f6e96610a4167b226cb926e2aa2b6b1d78057c576b"},
 ]
+fuuid = [
+    {file = "fuuid-0.1.0.tar.gz", hash = "sha256:ce8aec9ae81078941fa730dca0bf5ff7ca56675bea9327e938f1a04c8fad18b2"},
+]
 identify = [
     {file = "identify-2.2.10-py2.py3-none-any.whl", hash = "sha256:18d0c531ee3dbc112fa6181f34faa179de3f57ea57ae2899754f16a7e0ff6421"},
     {file = "identify-2.2.10.tar.gz", hash = "sha256:5b41f71471bc738e7b586308c3fca172f78940195cb3bf6734c1e66fdac49306"},
@@ -1009,8 +1095,12 @@ imagesize = [
     {file = "imagesize-1.2.0.tar.gz", hash = "sha256:b1f6b5a4eab1f73479a50fb79fcf729514a900c341d8503d62a62dbc4127a2b1"},
 ]
 importlib-metadata = [
-    {file = "importlib_metadata-4.6.0-py3-none-any.whl", hash = "sha256:c6513572926a96458f8c8f725bf0e00108fba0c9583ade9bd15b869c9d726e33"},
-    {file = "importlib_metadata-4.6.0.tar.gz", hash = "sha256:4a5611fea3768d3d967c447ab4e93f567d95db92225b43b7b238dbfb855d70bb"},
+    {file = "importlib_metadata-4.6.1-py3-none-any.whl", hash = "sha256:9f55f560e116f8643ecf2922d9cd3e1c7e8d52e683178fecd9d08f6aa357e11e"},
+    {file = "importlib_metadata-4.6.1.tar.gz", hash = "sha256:079ada16b7fc30dfbb5d13399a5113110dab1aa7c2bc62f66af75f0b717c8cac"},
+]
+iniconfig = [
+    {file = "iniconfig-1.1.1-py2.py3-none-any.whl", hash = "sha256:011e24c64b7f47f6ebd835bb12a743f2fbe9a26d4cecaa7f53bc4f35ee9da8b3"},
+    {file = "iniconfig-1.1.1.tar.gz", hash = "sha256:bc3af051d7d14b2ee5ef9969666def0cd1a000e121eaea580d4a313df4b37f32"},
 ]
 isort = [
     {file = "isort-5.9.1-py3-none-any.whl", hash = "sha256:8e2c107091cfec7286bc0f68a547d0ba4c094d460b732075b6fba674f1035c0c"},
@@ -1068,10 +1158,6 @@ mccabe = [
     {file = "mccabe-0.6.1-py2.py3-none-any.whl", hash = "sha256:ab8a6258860da4b6677da4bd2fe5dc2c659cff31b3ee4f7f5d64e79735b80d42"},
     {file = "mccabe-0.6.1.tar.gz", hash = "sha256:dd8d182285a0fe56bace7f45b5e7d1a6ebcbf524e8f3bd87eb0f125271b8831f"},
 ]
-more-itertools = [
-    {file = "more-itertools-8.8.0.tar.gz", hash = "sha256:83f0308e05477c68f56ea3a888172c78ed5d5b3c282addb67508e7ba6c8f813a"},
-    {file = "more_itertools-8.8.0-py3-none-any.whl", hash = "sha256:2cf89ec599962f2ddc4d568a05defc40e0a587fbc10d5989713638864c36be4d"},
-]
 multidict = [
     {file = "multidict-5.1.0-cp36-cp36m-macosx_10_14_x86_64.whl", hash = "sha256:b7993704f1a4b204e71debe6095150d43b2ee6150fa4f44d6d966ec356a8d61f"},
     {file = "multidict-5.1.0-cp36-cp36m-manylinux1_i686.whl", hash = "sha256:9dd6e9b1a913d096ac95d0399bd737e00f2af1e1594a787e00f7975778c8b2bf"},
@@ -1120,8 +1206,8 @@ nodeenv = [
     {file = "nodeenv-1.6.0.tar.gz", hash = "sha256:3ef13ff90291ba2a4a7a4ff9a979b63ffdd00a464dbe04acf0ea6471517a4c2b"},
 ]
 packaging = [
-    {file = "packaging-20.9-py2.py3-none-any.whl", hash = "sha256:67714da7f7bc052e064859c05c595155bd1ee9f69f76557e21f051443c20947a"},
-    {file = "packaging-20.9.tar.gz", hash = "sha256:5b327ac1320dc863dca72f4514ecc086f31186744b84a230374cc1fd776feae5"},
+    {file = "packaging-21.0-py3-none-any.whl", hash = "sha256:c86254f9220d55e31cc94d69bade760f0847da8000def4dfe1c6b872fd14ff14"},
+    {file = "packaging-21.0.tar.gz", hash = "sha256:7dc96269f53a4ccec5c0670940a4281106dd0bb343f47b7471f779df49c2fbe7"},
 ]
 pathspec = [
     {file = "pathspec-0.8.1-py2.py3-none-any.whl", hash = "sha256:aa0cb481c4041bf52ffa7b0d8fa6cd3e88a2ca4879c533c9153882ee2556790d"},
@@ -1156,13 +1242,23 @@ pyparsing = [
     {file = "pyparsing-2.4.7.tar.gz", hash = "sha256:c203ec8783bf771a155b207279b9bccb8dea02d8f0c9e5f8ead507bc3246ecc1"},
 ]
 pytest = [
-    {file = "pytest-4.6.11-py2.py3-none-any.whl", hash = "sha256:a00a7d79cbbdfa9d21e7d0298392a8dd4123316bfac545075e6f8f24c94d8c97"},
-    {file = "pytest-4.6.11.tar.gz", hash = "sha256:50fa82392f2120cc3ec2ca0a75ee615be4c479e66669789771f1758332be4353"},
+    {file = "pytest-6.2.4-py3-none-any.whl", hash = "sha256:91ef2131a9bd6be8f76f1f08eac5c5317221d6ad1e143ae03894b862e8976890"},
+    {file = "pytest-6.2.4.tar.gz", hash = "sha256:50bcad0a0b9c5a72c8e4e7c9855a3ad496ca6a881a3641b4260605450772c54b"},
+]
+pytest-cache = [
+    {file = "pytest-cache-1.0.tar.gz", hash = "sha256:be7468edd4d3d83f1e844959fd6e3fd28e77a481440a7118d430130ea31b07a9"},
 ]
 pytest-cov = [
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+    {file = "watchdog-2.1.3-cp38-cp38-macosx_11_0_arm64.whl", hash = "sha256:6fe9c8533e955c6589cfea6f3f0a1a95fb16867a211125236c82e1815932b5d7"},
+    {file = "watchdog-2.1.3-cp39-cp39-macosx_10_9_universal2.whl", hash = "sha256:d9456f0433845e7153b102fffeb767bde2406b76042f2216838af3b21707894e"},
+    {file = "watchdog-2.1.3-cp39-cp39-macosx_10_9_x86_64.whl", hash = "sha256:fd8c595d5a93abd441ee7c5bb3ff0d7170e79031520d113d6f401d0cf49d7c8f"},
+    {file = "watchdog-2.1.3-cp39-cp39-macosx_11_0_arm64.whl", hash = "sha256:0bcfe904c7d404eb6905f7106c54873503b442e8e918cc226e1828f498bdc0ca"},
+    {file = "watchdog-2.1.3-pp36-pypy36_pp73-macosx_10_9_x86_64.whl", hash = "sha256:bf84bd94cbaad8f6b9cbaeef43080920f4cb0e61ad90af7106b3de402f5fe127"},
+    {file = "watchdog-2.1.3-pp37-pypy37_pp73-macosx_10_9_x86_64.whl", hash = "sha256:b8ddb2c9f92e0c686ea77341dcb58216fa5ff7d5f992c7278ee8a392a06e86bb"},
+    {file = "watchdog-2.1.3-py3-none-manylinux2014_aarch64.whl", hash = "sha256:8805a5f468862daf1e4f4447b0ccf3acaff626eaa57fbb46d7960d1cf09f2e6d"},
+    {file = "watchdog-2.1.3-py3-none-manylinux2014_armv7l.whl", hash = "sha256:3e305ea2757f81d8ebd8559d1a944ed83e3ab1bdf68bcf16ec851b97c08dc035"},
+    {file = "watchdog-2.1.3-py3-none-manylinux2014_i686.whl", hash = "sha256:431a3ea70b20962e6dee65f0eeecd768cd3085ea613ccb9b53c8969de9f6ebd2"},
+    {file = "watchdog-2.1.3-py3-none-manylinux2014_ppc64.whl", hash = "sha256:e4929ac2aaa2e4f1a30a36751160be391911da463a8799460340901517298b13"},
+    {file = "watchdog-2.1.3-py3-none-manylinux2014_ppc64le.whl", hash = "sha256:201cadf0b8c11922f54ec97482f95b2aafca429c4c3a4bb869a14f3c20c32686"},
+    {file = "watchdog-2.1.3-py3-none-manylinux2014_s390x.whl", hash = "sha256:3a7d242a7963174684206093846537220ee37ba9986b824a326a8bb4ef329a33"},
+    {file = "watchdog-2.1.3-py3-none-manylinux2014_x86_64.whl", hash = "sha256:54e057727dd18bd01a3060dbf5104eb5a495ca26316487e0f32a394fd5fe725a"},
+    {file = "watchdog-2.1.3-py3-none-win32.whl", hash = "sha256:b5fc5c127bad6983eecf1ad117ab3418949f18af9c8758bd10158be3647298a9"},
+    {file = "watchdog-2.1.3-py3-none-win_amd64.whl", hash = "sha256:44acad6f642996a2b50bb9ce4fb3730dde08f23e79e20cd3d8e2a2076b730381"},
+    {file = "watchdog-2.1.3-py3-none-win_ia64.whl", hash = "sha256:0bcdf7b99b56a3ae069866c33d247c9994ffde91b620eaf0306b27e099bd1ae0"},
+    {file = "watchdog-2.1.3.tar.gz", hash = "sha256:e5236a8e8602ab6db4b873664c2d356c365ab3cac96fbdec4970ad616415dd45"},
 ]
 yarl = [
     {file = "yarl-1.6.3-cp36-cp36m-macosx_10_14_x86_64.whl", hash = "sha256:0355a701b3998dcd832d0dc47cc5dedf3874f966ac7f870e0f3a6788d802d434"},
@@ -1394,6 +1509,6 @@ yarl = [
     {file = "yarl-1.6.3.tar.gz", hash = "sha256:8a9066529240171b68893d60dca86a763eae2139dd42f42106b03cf4b426bf10"},
 ]
 zipp = [
-    {file = "zipp-3.4.1-py3-none-any.whl", hash = "sha256:51cb66cc54621609dd593d1787f286ee42a5c0adbb4b29abea5a63edc3e03098"},
-    {file = "zipp-3.4.1.tar.gz", hash = "sha256:3607921face881ba3e026887d8150cca609d517579abe052ac81fc5aeffdbd76"},
+    {file = "zipp-3.5.0-py3-none-any.whl", hash = "sha256:957cfda87797e389580cb8b9e3870841ca991e2125350677b2ca83a0e99390a3"},
+    {file = "zipp-3.5.0.tar.gz", hash = "sha256:f5812b1e007e48cff63449a5e9f4e7ebea716b4111f9c4f9a645f91d579bf0c4"},
 ]
diff --git a/pyproject.toml b/pyproject.toml
index c554a19..1270093 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -13,19 +13,23 @@ aiohttp = "^3.7.4"
 requests = "^2.25.1"
 python-dotenv = "^0.15.0"
 dataclasses-json = "^0.5.3"
+fuuid = "^0.1.0"
 
 [tool.poetry.dev-dependencies]
-pytest = "^4.6"
+pytest = ">=5.0"
+pytest-cov = "^2.11.1"
+pytest-mock = "^3.6.1"
 black = "^20.8b1"
 flake8 = "^3.8.4"
 Sphinx = "^3.5.2"
 tox = "^3.23.0"
 coverage = "^5.5"
-pytest-cov = "^2.11.1"
 isort = "^5.8.0"
 responses = "^0.13.3"
 coveralls = "^3.1.0"
 pre-commit = "2.13.0"
+pytest-cache = "^1.0"
+pytest-watch = "^4.2.0"
 
 [tool.black]
 line-length = 100
diff --git a/requirements.txt b/requirements.txt
index 5763db5..ec44660 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,52 +2,58 @@ aiohttp==3.7.4.post0; python_version >= "3.6"
 alabaster==0.7.12; python_version >= "3.5"
 appdirs==1.4.4; python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6"
 async-timeout==3.0.1; python_full_version >= "3.5.3" and python_version >= "3.6"
-atomicwrites==1.4.0; python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0"
+atomicwrites==1.4.0; python_version >= "3.6" and python_full_version < "3.0.0" and sys_platform == "win32" and (python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6") or sys_platform == "win32" and python_version >= "3.6" and python_full_version >= "3.4.0" and (python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6")
 attrs==21.2.0; python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6"
 babel==2.9.1; python_version >= "3.5" and python_full_version < "3.0.0" or python_full_version >= "3.4.0" and python_version >= "3.5"
+base58==2.1.0; python_version >= "3.7" and python_version < "4.0"
 black==20.8b1; python_version >= "3.6"
 certifi==2021.5.30; python_version >= "3.5" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.5"
 cfgv==3.3.0; python_full_version >= "3.6.1"
 chardet==4.0.0; python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6"
 click==8.0.1; python_version >= "3.6"
-colorama==0.4.4; python_version >= "3.6" and python_full_version < "3.0.0" and sys_platform == "win32" and (python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.4.0") and platform_system == "Windows" and (python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0") or sys_platform == "win32" and python_version >= "3.6" and (python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.4.0") and python_full_version >= "3.5.0" and platform_system == "Windows" and (python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0")
+colorama==0.4.4; python_version >= "3.6" and python_full_version < "3.0.0" and sys_platform == "win32" and platform_system == "Windows" and (python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6") or sys_platform == "win32" and python_version >= "3.6" and python_full_version >= "3.5.0" and platform_system == "Windows" and (python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6")
 coverage==5.5; (python_version >= "2.7" and python_full_version < "3.0.0") or (python_full_version >= "3.5.0" and python_version < "4")
 coveralls==3.1.0; python_version >= "3.5"
 dataclasses-json==0.5.4; python_version >= "3.6"
 distlib==0.3.2; python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0"
 docopt==0.6.2; python_version >= "3.5"
 docutils==0.16; python_version >= "3.5" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.5"
+execnet==1.9.0; python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0"
 filelock==3.0.12; python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0"
 flake8==3.9.2; (python_version >= "2.7" and python_full_version < "3.0.0") or (python_full_version >= "3.5.0")
+fuuid==0.1.0; python_version >= "3.7" and python_version < "4.0"
 identify==2.2.10; python_full_version >= "3.6.1"
 idna==2.10; python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6"
 imagesize==1.2.0; python_version >= "3.5" and python_full_version < "3.0.0" or python_full_version >= "3.4.0" and python_version >= "3.5"
-importlib-metadata==4.6.0; python_full_version >= "3.6.1" and python_version < "3.8" and python_version >= "3.6" and (python_version >= "3.6" and python_full_version < "3.0.0" and python_version < "3.8" or python_full_version >= "3.4.0" and python_version < "3.8" and python_version >= "3.6") and (python_version >= "3.6" and python_full_version < "3.0.0" and python_version < "3.8" or python_full_version >= "3.5.0" and python_version < "3.8" and python_version >= "3.6")
+importlib-metadata==4.6.1; python_version < "3.8" and python_version >= "3.6" and (python_version >= "3.6" and python_full_version < "3.0.0" and python_version < "3.8" or python_full_version >= "3.5.0" and python_version < "3.8" and python_version >= "3.6") and python_full_version >= "3.6.1" and (python_version >= "3.6" and python_full_version < "3.0.0" and python_version < "3.8" or python_full_version >= "3.4.0" and python_version >= "3.6" and python_version < "3.8") and (python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6")
+iniconfig==1.1.1; python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6"
 isort==5.9.1; python_full_version >= "3.6.1" and python_version < "4.0"
 jinja2==3.0.1; python_version >= "3.6"
 markupsafe==2.0.1; python_version >= "3.6"
 marshmallow==3.12.1; python_version >= "3.6"
 marshmallow-enum==1.5.1; python_version >= "3.6"
 mccabe==0.6.1; python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0"
-more-itertools==8.8.0; python_version >= "3.5" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.5"
 multidict==5.1.0; python_version >= "3.6"
 mypy-extensions==0.4.3; python_version >= "3.6"
 nodeenv==1.6.0; python_full_version >= "3.6.1"
-packaging==20.9; python_version >= "3.5" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.5"
+packaging==21.0; python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6"
 pathspec==0.8.1; python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6"
-pluggy==0.13.1; python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0"
+pluggy==0.13.1; python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6"
 pre-commit==2.13.0; python_full_version >= "3.6.1"
-py==1.10.0; python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0"
+py==1.10.0; python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6"
 pycodestyle==2.7.0; python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0"
 pyflakes==2.3.1; python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0"
 pygments==2.9.0; python_version >= "3.5"
-pyparsing==2.4.7; python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.4.0"
-pytest==4.6.11; (python_version >= "2.7" and python_full_version < "3.0.0") or (python_full_version >= "3.4.0")
+pyparsing==2.4.7; python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.3.0" and python_version >= "3.6"
+pytest==6.2.4; python_version >= "3.6"
+pytest-cache==1.0
 pytest-cov==2.12.1; (python_version >= "2.7" and python_full_version < "3.0.0") or (python_full_version >= "3.5.0")
+pytest-mock==3.6.1; python_version >= "3.6"
+pytest-watch==4.2.0
 python-dotenv==0.15.0
 pytz==2021.1; python_version >= "3.5" and python_full_version < "3.0.0" or python_full_version >= "3.4.0" and python_version >= "3.5"
 pyyaml==5.4.1; python_full_version >= "3.6.1"
-regex==2021.4.4; python_version >= "3.6"
+regex==2021.7.6; python_version >= "3.6"
 requests==2.25.1; (python_version >= "2.7" and python_full_version < "3.0.0") or (python_full_version >= "3.5.0")
 responses==0.13.3; (python_version >= "2.7" and python_full_version < "3.0.0") or (python_full_version >= "3.5.0")
 six==1.16.0; python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0"
@@ -60,13 +66,13 @@ sphinxcontrib-jsmath==1.0.1; python_version >= "3.5"
 sphinxcontrib-qthelp==1.0.3; python_version >= "3.5"
 sphinxcontrib-serializinghtml==1.1.5; python_version >= "3.5"
 stringcase==1.2.0; python_version >= "3.6"
-toml==0.10.2; python_full_version >= "3.6.1" and python_version >= "3.6"
+toml==0.10.2; python_full_version >= "3.6.1" and python_version >= "3.6" and (python_version >= "3.6" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version >= "3.6")
 tox==3.23.1; (python_version >= "2.7" and python_full_version < "3.0.0") or (python_full_version >= "3.5.0")
 typed-ast==1.4.3; python_version >= "3.6"
-typing-extensions==3.10.0.0; python_version < "3.8" and python_version >= "3.6" and (python_version >= "3.6" and python_full_version < "3.0.0" and python_version < "3.8" or python_full_version >= "3.4.0" and python_version < "3.8" and python_version >= "3.6")
+typing-extensions==3.10.0.0; python_version < "3.8" and python_version >= "3.6"
 typing-inspect==0.7.1; python_version >= "3.6"
 urllib3==1.26.6; python_version >= "3.5" and python_full_version < "3.0.0" or python_full_version >= "3.5.0" and python_version < "4" and python_version >= "3.5"
 virtualenv==20.4.7; python_full_version >= "3.6.1"
-wcwidth==0.2.5; python_version >= "2.7" and python_full_version < "3.0.0" or python_full_version >= "3.5.0"
+watchdog==2.1.3; python_version >= "3.6"
 yarl==1.6.3; python_version >= "3.6"
-zipp==3.4.1; python_version >= "3.6" and python_full_version < "3.0.0" and python_version < "3.8" or python_full_version >= "3.4.0" and python_version < "3.8" and python_version >= "3.6"
+zipp==3.5.0; python_version < "3.8" and python_version >= "3.6"
diff --git a/shipengine_sdk/events/__init__.py b/shipengine_sdk/events/__init__.py
new file mode 100644
index 0000000..d0a5cde
--- /dev/null
+++ b/shipengine_sdk/events/__init__.py
@@ -0,0 +1,203 @@
+"""
+ShipEngine event emission via Observer Pattern. The ShipEngine SDK emits when an
+HTTP request is sent and when an HTTP response is received for said request.
+"""
+import json
+from dataclasses import dataclass
+from datetime import datetime
+from typing import Any, Callable, Dict, List, Optional, Union
+
+from dataclasses_json import dataclass_json
+
+from ..errors import ShipEngineError
+from ..models.enums import Events
+
+
+class ShipEngineEvent:
+    timestamp: datetime
+
+    def __init__(self, event_type: str, message: str) -> None:
+        self.timestamp = datetime.now()
+        self.type = event_type
+        self.message = message
+
+    def to_dict(self):
+        return (lambda o: o.__dict__)(self)
+
+    def to_json(self):
+        return json.dumps(self, default=lambda o: o.__dict__, indent=2)
+
+    @staticmethod
+    def new_event_message(method: str, base_uri: str, message_type: str) -> str:
+        """A method to dynamically create an event message based on the $messageType being passed in."""
+        if message_type == "base_message":
+            return f"Calling the ShipEngine {method} API at {base_uri}"
+        elif message_type == "retry_message":
+            return f"Retrying the ShipEngine {method} API at {base_uri}"
+        else:
+            raise ShipEngineError(f"Message type [{message_type}] is not a valid type of message.")
+
+
+class RequestSentEvent(ShipEngineEvent):
+    REQUEST_SENT = "request_sent"
+
+    def __init__(
+        self,
+        request_id: str,
+        message: str,
+        base_uri: str,
+        headers: List[str],
+        body: Dict[str, Any],
+        retry: int,
+        timeout: int,
+    ) -> None:
+        super().__init__(event_type=self.REQUEST_SENT, message=message)
+        self.request_id = request_id
+        self.base_uri = base_uri
+        self.headers = headers
+        self.body = body
+        self.retry = retry
+        self.timeout = timeout
+
+
+class ResponseReceivedEvent(ShipEngineEvent):
+    RESPONSE_RECEIVED = "response_received"
+
+    def __init__(
+        self,
+        message: str,
+        request_id: str,
+        base_uri: str,
+        status_code: int,
+        headers: List[str],
+        body: Dict[str, Any],
+        retry: int,
+        elapsed: float,
+    ) -> None:
+        super().__init__(event_type=self.RESPONSE_RECEIVED, message=message)
+        self.request_id = request_id
+        self.base_uri = base_uri
+        self.status_code = status_code
+        self.headers = headers
+        self.body = body
+        self.retry = retry
+        self.elapsed = elapsed
+
+
+class Dispatcher:
+    def __init__(self, events: Optional[List[str]] = None) -> None:
+        events_list = [Events.ON_REQUEST_SENT.value, Events.ON_RESPONSE_RECEIVED.value]
+        if events:
+            for i in events:
+                events_list.append(i)
+
+        self.events = {event: dict() for event in events_list}
+
+    def get_subscribers(self, event: Optional[str] = None):
+        return self.events[event]
+
+    def register(self, event, subscriber, callback: Union[Callable, str] = None):
+        if event is Events.ON_REQUEST_SENT.value and callback is None:
+            callback = getattr(subscriber, "catch_request_sent_event")
+        elif event is Events.ON_RESPONSE_RECEIVED.value and callback is None:
+            callback = getattr(subscriber, "catch_response_received_event")
+        self.get_subscribers(event)[subscriber] = callback
+
+    def unregister(self, event, subscriber):
+        del self.get_subscribers(event)[subscriber]
+
+    def dispatch(self, event, event_name: str = None):
+        for subscriber, callback in self.get_subscribers(event_name).items():
+            callback(event)
+
+    def to_dict(self):
+        return (lambda o: o.__dict__)(self)
+
+    def to_json(self):
+        return json.dumps(self, default=lambda o: o.__dict__, indent=2)
+
+
+class Subscriber:
+    def __init__(self, name=None) -> None:
+        if name is not None:
+            self.name = name
+        else:
+            self.name = "Event Subscriber"
+
+    @staticmethod
+    def update(event: Union[RequestSentEvent, ResponseReceivedEvent]):
+        return event
+
+    @staticmethod
+    def catch_request_sent_event(event: RequestSentEvent):
+        return event
+
+    @staticmethod
+    def catch_response_received_event(event: ResponseReceivedEvent):
+        return event
+
+    def to_dict(self):
+        return (lambda o: o.__dict__)(self)
+
+    def to_json(self):
+        return json.dumps(self, default=lambda o: o.__dict__, indent=2)
+
+
+class ShipEngineEventListener(Subscriber):
+    def __init__(self, name=None) -> None:
+        super().__init__(name=name)
+
+    # You can add your own event consumption logic by adding/overriding the parent `update()` method below.
+    @staticmethod
+    def update(event: Union[RequestSentEvent, ResponseReceivedEvent]):
+        # print(event.to_dict())
+        return event
+
+
+def emit_event(emitted_event_type: str, event_data, dispatcher: Dispatcher):
+    if emitted_event_type == RequestSentEvent.REQUEST_SENT:
+        request_sent_event = RequestSentEvent(
+            message=event_data.message,
+            request_id=event_data.id,
+            base_uri=event_data.base_uri,
+            headers=event_data.request_headers,
+            body=event_data.body,
+            retry=event_data.retry,
+            timeout=event_data.timeout,
+        )
+        dispatcher.dispatch(event=request_sent_event, event_name=Events.ON_REQUEST_SENT.value)
+        return request_sent_event
+    elif emitted_event_type == ResponseReceivedEvent.RESPONSE_RECEIVED:
+        response_received_event = ResponseReceivedEvent(
+            message=event_data.message,
+            request_id=event_data.id,
+            base_uri=event_data.base_uri,
+            status_code=event_data.status_code,
+            headers=event_data.response_headers,
+            body=event_data.body,
+            retry=event_data.retry,
+            elapsed=event_data.elapsed,
+        )
+        dispatcher.dispatch(
+            event=response_received_event, event_name=Events.ON_RESPONSE_RECEIVED.value
+        )
+        return response_received_event
+    else:
+        raise ShipEngineError(f"Event type [{emitted_event_type}] is not a valid type of event.")
+
+
+@dataclass_json
+@dataclass
+class EventOptions:
+    """To be used as the main argument in the **emitEvent()** function."""
+
+    message: Optional[str]
+    id: Optional[str]
+    base_uri: Optional[str]
+    body: Optional[Dict[str, Any]]
+    retry: Optional[int]
+    status_code: Optional[int] = None
+    request_headers: Optional[Dict[str, Any]] = None
+    response_headers: Any = None
+    timeout: Optional[int] = None
+    elapsed: Optional[float] = None
diff --git a/shipengine_sdk/http_client/client.py b/shipengine_sdk/http_client/client.py
index 2a13aa0..ae2bf2a 100644
--- a/shipengine_sdk/http_client/client.py
+++ b/shipengine_sdk/http_client/client.py
@@ -2,6 +2,7 @@
 import json
 import os
 import platform
+from datetime import datetime
 from typing import Any, Dict, Optional
 
 import requests
@@ -13,10 +14,55 @@
 from shipengine_sdk import __version__
 
 from ..errors import ShipEngineError
+from ..events import (
+    Dispatcher,
+    EventOptions,
+    RequestSentEvent,
+    ResponseReceivedEvent,
+    ShipEngineEvent,
+    emit_event,
+)
 from ..jsonrpc.process_request import handle_response, wrap_request
 from ..models import ErrorCode, ErrorSource, ErrorType
+from ..models.enums import Events
 from ..shipengine_config import ShipEngineConfig
-from ..util.sdk_assertions import is_response_404, is_response_429, is_response_500
+from ..util.sdk_assertions import check_response_for_errors
+
+
+def base_url(config) -> str:
+    return config.base_uri if os.getenv("CLIENT_BASE_URI") is None else os.getenv("CLIENT_BASE_URI")
+
+
+def generate_event_message(
+    retry: int,
+    method: str,
+    base_uri: str,
+    status_code: Optional[int] = None,
+    message_type: Optional[str] = None,
+) -> str:
+    if message_type == "received":
+        if retry > 0:
+            f"Retrying the ShipEngine {method} API at {base_uri}"
+        else:
+            return f"Received an HTTP {status_code} response from the ShipEngine {method} API"
+
+    if retry == 0:
+        return ShipEngineEvent.new_event_message(
+            method=method, base_uri=base_uri, message_type="base_message"
+        )
+    else:
+        return ShipEngineEvent.new_event_message(
+            method=method, base_uri=base_uri, message_type="retry_message"
+        )
+
+
+def request_headers(user_agent: str, api_key: str) -> Dict[str, Any]:
+    return {
+        "User-Agent": user_agent,
+        "Content-Type": "application/json",
+        "Accept": "application/json",
+        "Api-Key": api_key,
+    }
 
 
 class ShipEngineAuth(AuthBase):
@@ -30,10 +76,16 @@ def __call__(self, request: Request, *args, **kwargs) -> Request:
 
 
 class ShipEngineClient:
-    _BASE_URI: str = ""
+    _DISPATCHER: Dispatcher = Dispatcher()
 
-    def __init__(self) -> None:
+    def __init__(self, config: ShipEngineConfig) -> None:
         """A `JSON-RPC 2.0` HTTP client used to send all HTTP requests from the SDK."""
+        self._DISPATCHER.register(
+            event=Events.ON_REQUEST_SENT.value, subscriber=config.event_listener
+        )
+        self._DISPATCHER.register(
+            event=Events.ON_RESPONSE_RECEIVED.value, subscriber=config.event_listener
+        )
         self.session = requests.session()
 
     def send_rpc_request(
@@ -44,29 +96,38 @@ def send_rpc_request(
          * is successful, the result is returned. Otherwise, an error is thrown.
         """
         client: Session = self._request_retry_session(retries=config.retries)
-        base_uri: Optional[str] = (
-            config.base_uri
-            if os.getenv("CLIENT_BASE_URI") is None
-            else os.getenv("CLIENT_BASE_URI")
-        )
-
-        request_headers: Dict[str, Any] = {
-            "User-Agent": self._derive_user_agent(),
-            "Content-Type": "application/json",
-            "Accept": "application/json",
-        }
+        base_uri = base_url(config=config)
 
         request_body: Dict[str, Any] = wrap_request(method=method, params=params)
-
+        req_headers = request_headers(user_agent=self._derive_user_agent(), api_key=config.api_key)
         req: Request = Request(
             method="POST",
             url=base_uri,
             data=json.dumps(request_body),
-            headers=request_headers,
+            headers=req_headers,
             auth=ShipEngineAuth(config.api_key),
         )
         prepared_req: PreparedRequest = req.prepare()
 
+        request_event_message = generate_event_message(
+            retry=retry, method=method, base_uri=base_uri
+        )
+
+        request_event_data = EventOptions(
+            message=request_event_message,
+            id=request_body["id"],
+            base_uri=base_uri,
+            request_headers=req_headers,
+            body=request_body,
+            retry=retry,
+            timeout=config.timeout,
+        )
+        request_sent_event = emit_event(
+            emitted_event_type=RequestSentEvent.REQUEST_SENT,
+            event_data=request_event_data,
+            dispatcher=self._DISPATCHER,
+        )
+
         try:
             resp: Response = client.send(request=prepared_req, timeout=config.timeout)
         except RequestException as err:
@@ -80,10 +141,32 @@ def send_rpc_request(
         resp_body: Dict[str, Any] = resp.json()
         status_code: int = resp.status_code
 
-        is_response_404(status_code=status_code, response_body=resp_body, config=config)
-        is_response_429(status_code=status_code, response_body=resp_body, config=config)
-        is_response_500(status_code=status_code, response_body=resp_body)
+        response_received_message = generate_event_message(
+            retry=retry,
+            method=method,
+            base_uri=base_uri,
+            status_code=status_code,
+            message_type="received",
+        )
+        response_event_data = EventOptions(
+            message=response_received_message,
+            id=request_body["id"],
+            base_uri=base_uri,
+            status_code=status_code,
+            response_headers=resp.headers,
+            body=request_body,
+            retry=retry,
+            elapsed=(request_sent_event.timestamp - datetime.now()).total_seconds(),
+        )
+
+        # Emit `ResponseReceivedEvent` to registered Subscribers.
+        emit_event(
+            emitted_event_type=ResponseReceivedEvent.RESPONSE_RECEIVED,
+            event_data=response_event_data,
+            dispatcher=self._DISPATCHER,
+        )
 
+        check_response_for_errors(status_code=status_code, response_body=resp_body, config=config)
         return handle_response(resp.json())
 
     def _request_retry_session(
@@ -112,8 +195,7 @@ def _derive_user_agent() -> str:
         :rtype: str
         """
         sdk_version: str = f"shipengine-python/{__version__}"
-        os_kernel: str = platform.platform(terse=True)
         python_version: str = platform.python_version()
         python_implementation: str = platform.python_implementation()
 
-        return f"{sdk_version} {os_kernel} {python_version} {python_implementation}"
+        return f"{sdk_version} {python_implementation}-v{python_version}"
diff --git a/shipengine_sdk/jsonrpc/__init__.py b/shipengine_sdk/jsonrpc/__init__.py
index d25f3b4..7502077 100644
--- a/shipengine_sdk/jsonrpc/__init__.py
+++ b/shipengine_sdk/jsonrpc/__init__.py
@@ -21,8 +21,7 @@ def rpc_request(
 def rpc_request_loop(
     method: str, params: Optional[Dict[str, Any]], config: ShipEngineConfig
 ) -> Dict[str, Any]:
-    client: ShipEngineClient = ShipEngineClient()
-    api_response: Optional[Dict[str, Any]] = None
+    client: ShipEngineClient = ShipEngineClient(config=config)
     retry: int = 0
     while retry <= config.retries:
         try:
@@ -36,7 +35,8 @@ def rpc_request_loop(
                 and err.retry_after < config.timeout
             ):
                 time.sleep(err.retry_after)
+                retry += 1
+                continue
             else:
                 raise err
-        retry += 1
         return api_response
diff --git a/shipengine_sdk/jsonrpc/process_request.py b/shipengine_sdk/jsonrpc/process_request.py
index a7d59df..05fa692 100644
--- a/shipengine_sdk/jsonrpc/process_request.py
+++ b/shipengine_sdk/jsonrpc/process_request.py
@@ -1,6 +1,7 @@
 """Functions that help with process requests and handle responses."""
 from typing import Any, Dict, Optional
-from uuid import uuid4
+
+from fuuid import b58_fuuid
 
 from ..errors import (
     AccountStatusError,
@@ -24,11 +25,9 @@ def wrap_request(method: str, params: Optional[Dict[str, Any]]) -> Dict[str, Any
     :type params: Optional[Dict[str, Any]]
     """
     if params is None:
-        return dict(id=f"req_{str(uuid4()).replace('-', '')}", jsonrpc="2.0", method=method)
+        return dict(id=f"req_{b58_fuuid()}", jsonrpc="2.0", method=method)
     else:
-        return dict(
-            id=f"req_{str(uuid4()).replace('-', '')}", jsonrpc="2.0", method=method, params=params
-        )
+        return dict(id=f"req_{b58_fuuid()}", jsonrpc="2.0", method=method, params=params)
 
 
 def handle_response(response_body: Dict[str, Any]) -> Dict[str, Any]:
diff --git a/shipengine_sdk/models/address/__init__.py b/shipengine_sdk/models/address/__init__.py
index 7061a10..a47a399 100644
--- a/shipengine_sdk/models/address/__init__.py
+++ b/shipengine_sdk/models/address/__init__.py
@@ -22,10 +22,10 @@ class Address:
     state_province: str
     postal_code: str
     country_code: str
-    is_residential: Optional[bool] = None
-    name: str = ""
-    phone: str = ""
-    company: str = ""
+    is_residential: Optional[bool] = False
+    name: Optional[str] = ""
+    phone: Optional[str] = ""
+    company: Optional[str] = ""
 
     def __post_init__(self) -> None:
         is_street_valid(self.street)
diff --git a/shipengine_sdk/models/carriers/__init__.py b/shipengine_sdk/models/carriers/__init__.py
index 90f958e..a7c04fd 100644
--- a/shipengine_sdk/models/carriers/__init__.py
+++ b/shipengine_sdk/models/carriers/__init__.py
@@ -31,7 +31,7 @@ class CarrierAccount:
     def __init__(self, account_information: Dict[str, Any]) -> None:
         """This class represents a given account with a Carrier provider e.g. `FedEx`, `UPS`, `USPS`."""
         self._set_carrier(account_information["carrierCode"])
-        self.account_id = account_information["accountID"]
+        self.account_id = account_information["accountId"]
         self.account_number = account_information["accountNumber"]
 
     def _set_carrier(self, carrier: str) -> None:
diff --git a/shipengine_sdk/models/enums/__init__.py b/shipengine_sdk/models/enums/__init__.py
index 9badc5a..be38bf1 100644
--- a/shipengine_sdk/models/enums/__init__.py
+++ b/shipengine_sdk/models/enums/__init__.py
@@ -9,13 +9,26 @@
 from .regex_patterns import RegexPatterns
 
 
+class Constants(Enum):
+    """Test API Key for use with Simengine."""
+
+    STUB_API_KEY = "TEST_vMiVbICUjBz4BZjq0TRBLC/9MrxY4+yjvb1G1RMxlJs"
+    CARRIER_ACCOUNT_ID_STUB = "car_41GrQHn5uouiPZc2TNE6PU29tZU9ud"
+
+
 class Endpoints(Enum):
     """API Endpoint URI's used throughout the ShipEngine SDK."""
 
-    TEST_RPC_URL = "https://simengine.herokuapp.com/jsonrpc"
     SHIPENGINE_RPC_URL = "https://api.shipengine.com/jsonrpc"
 
 
+class Events(Enum):
+    """ShipEngine Events emitted by the SDK when a request is sent or when a response is received."""
+
+    ON_REQUEST_SENT = "on_request_sent"
+    ON_RESPONSE_RECEIVED = "on_response_received"
+
+
 class RPCMethods(Enum):
     """A collection of RPC Methods used throughout the ShipEngine SDK."""
 
diff --git a/shipengine_sdk/models/package/__init__.py b/shipengine_sdk/models/package/__init__.py
index 432526d..daeeff0 100644
--- a/shipengine_sdk/models/package/__init__.py
+++ b/shipengine_sdk/models/package/__init__.py
@@ -17,7 +17,7 @@ class Shipment:
     shipment_id: Optional[str] = None
     account_id: Optional[str] = None
     carrier_account: Optional[CarrierAccount] = None
-    carrier: Carrier
+    carrier: Optional[Carrier] = None
     estimated_delivery_date: Union[IsoString, str]
     actual_delivery_date: Union[IsoString, str]
 
@@ -26,8 +26,8 @@ def __init__(
     ) -> None:
         """This object represents a given Shipment."""
         self.config = config
-        self.shipment_id = shipment["shipmentID"] if "shipmentID" in shipment else None
-        self.account_id = shipment["carrierAccountID"] if "carrierAccountID" in shipment else None
+        self.shipment_id = shipment["shipmentId"] if "shipmentId" in shipment else None
+        self.account_id = shipment["carrierAccountId"] if "carrierAccountId" in shipment else None
 
         if self.account_id is not None:
             self.carrier_account = self._get_carrier_account(
@@ -59,7 +59,7 @@ def _get_carrier_account(self, carrier: str, account_id: str) -> CarrierAccount:
                 return target_carrier[0]
 
         raise ShipEngineError(
-            message=f"accountID [{account_id}] doesn't match any of the accounts connected to your ShipEngine Account."  # noqa
+            message=f"accountId [{account_id}] doesn't match any of the accounts connected to your ShipEngine Account."  # noqa
         )
 
     def to_dict(self) -> Dict[str, Any]:
@@ -77,7 +77,7 @@ def to_json(self) -> str:
         return json.dumps(self, default=lambda o: o.__dict__, indent=2)
 
     def __repr__(self):
-        return f"Shipment({self.shipment_id}, {self.account_id}, {self.carrier_account}, {self.carrier}, {self.estimated_delivery_date}, {self.actual_delivery_date})"  # noqa
+        return f"Shipment({self.shipment_id}, {self.account_id})"
 
 
 class Package:
@@ -90,11 +90,11 @@ class Package:
     tracking_url: Optional[str]
 
     def __init__(self, package: Dict[str, Any]) -> None:
-        self.package_id = package["packageID"] if "packageID" in package else None
+        self.package_id = package["packageId"] if "packageId" in package else None
         self.weight = package["weight"] if "weight" in package else None
         self.dimensions = package["dimensions"] if "dimensions" in package else None
         self.tracking_number = package["trackingNumber"] if "trackingNumber" in package else None
-        self.tracking_url = package["trackingURL"] if "trackingURL" in package else None
+        self.tracking_url = package["trackingUrl"] if "trackingUrl" in package else None
 
     def to_dict(self) -> Dict[str, Any]:
         return (lambda o: o.__dict__)(self)
@@ -125,15 +125,31 @@ class Location:
 
     def __init__(self, location_data: Dict[str, Any]) -> None:
         self.city_locality = (
-            location_data["cityLocality"] if "cityLocality" in location_data else None
+            location_data["cityLocality"]
+            if "cityLocality" in location_data and location_data is not None
+            else None
         )
         self.state_province = (
-            location_data["stateProvince"] if "stateProvince" in location_data else None
+            location_data["stateProvince"]
+            if "stateProvince" in location_data and location_data is not None
+            else None
+        )
+        self.postal_code = (
+            location_data["postalCode"]
+            if "postalCode" in location_data and location_data is not None
+            else None
+        )
+        self.country_code = (
+            location_data["countryCode"]
+            if "countryCode" in location_data and location_data is not None
+            else None
         )
-        self.postal_code = location_data["postalCode"] if "postalCode" in location_data else None
-        self.country_code = location_data["countryCode"] if "countryCode" in location_data else None
 
-        if "coordinates" in location_data:
+        if (
+            "coordinates" in location_data
+            and location_data is not None
+            and location_data["coordinates"] is not None
+        ):
             self.latitude = location_data["coordinates"]["latitude"]
             self.longitude = location_data["coordinates"]["longitude"]
 
@@ -168,8 +184,15 @@ def __init__(self, event: Dict[str, Any]) -> None:
         self.carrier_status_code = (
             event["carrierStatusCode"] if "carrierStatusCode" in event else None
         )
+        self.carrier_detail_code = (
+            event["carrierDetailCode"] if "carrierDetailCode" in event else None
+        )
         self.signer = event["signer"] if "signer" in event else None
-        self.location = Location(event["location"]) if "location" in event else None
+        self.location = (
+            Location(event["location"])
+            if "location" in event and event["location"] is not None
+            else None
+        )
 
     def to_dict(self):
         return (lambda o: o.__dict__)(self)
diff --git a/shipengine_sdk/services/address_validation.py b/shipengine_sdk/services/address_validation.py
index f38318d..31b4552 100644
--- a/shipengine_sdk/services/address_validation.py
+++ b/shipengine_sdk/services/address_validation.py
@@ -20,14 +20,14 @@ def validate(address: Address, config: ShipEngineConfig) -> AddressValidateResul
     api_response: Dict[str, Any] = rpc_request(
         method=RPCMethods.ADDRESS_VALIDATE.value,
         config=config,
-        params={"address": address.to_dict()},  # type: ignore
+        params={"address": address.to_dict()},
     )
     result: Dict[str, Any] = api_response["result"]
     return AddressValidateResult(
         is_valid=result["isValid"],
         request_id=api_response["id"],
         normalized_address=Address.from_dict(result["normalizedAddress"])
-        if "normalizedAddress" in result
+        if "normalizedAddress" in result and result["normalizedAddress"] is not None
         else None,
         messages=result["messages"],
     )
diff --git a/shipengine_sdk/services/track_package.py b/shipengine_sdk/services/track_package.py
index c862efd..764d6c2 100644
--- a/shipengine_sdk/services/track_package.py
+++ b/shipengine_sdk/services/track_package.py
@@ -14,7 +14,7 @@ def track(tracking_data: Union[str, TrackingQuery], config: ShipEngineConfig) ->
         api_response = rpc_request(
             method=RPCMethods.TRACK_PACKAGE.value,
             config=config,
-            params={"packageID": tracking_data},
+            params={"packageId": tracking_data},
         )
 
         return TrackPackageResult(api_response, config)
diff --git a/shipengine_sdk/shipengine_config.py b/shipengine_sdk/shipengine_config.py
index 5649b1b..596bbc1 100644
--- a/shipengine_sdk/shipengine_config.py
+++ b/shipengine_sdk/shipengine_config.py
@@ -2,6 +2,7 @@
 import json
 from typing import Any, Dict, Optional
 
+from .events import ShipEngineEventListener
 from .models import Endpoints
 from .util import is_api_key_valid, is_retries_valid, is_timeout_valid
 
@@ -48,7 +49,11 @@ def __init__(self, config: Dict[str, Any]) -> None:
             self.retries: int = config["retries"]
         else:
             self.retries: int = self.DEFAULT_RETRIES
-        # TODO: add event listener to config object once it"s implemented.
+
+        if "event_listener" in config:
+            self.event_listener = config["event_listener"]
+        else:
+            self.event_listener = ShipEngineEventListener()
 
     def merge(self, new_config: Optional[Dict[str, Any]] = None):
         """
@@ -79,7 +84,12 @@ def merge(self, new_config: Optional[Dict[str, Any]] = None):
             config.update(
                 {"timeout": new_config["timeout"]}
             ) if "timeout" in new_config else config.update({"timeout": self.timeout})
-            # TODO: added merge rule for event_listener once it is implemented.
+
+            config.update(
+                {"event_listener": new_config["event_listener"]}
+            ) if "event_listener" in new_config else config.update(
+                {"event_listener": self.event_listener}
+            )
 
             return ShipEngineConfig(config)
 
diff --git a/shipengine_sdk/util/iso_string.py b/shipengine_sdk/util/iso_string.py
index 3d660a4..cdd02e3 100644
--- a/shipengine_sdk/util/iso_string.py
+++ b/shipengine_sdk/util/iso_string.py
@@ -11,9 +11,7 @@ def __init__(self, iso_string: str) -> None:
         A string representing a Date, DateTime, or DateTime with Timezone. The object
         also has a method to return a `datetime.datetime` object, which is the native
         datetime object in python as of 3.7.
-
         This class object takes in an **ISO-8601** string. Learn more here: https://en.wikipedia.org/wiki/ISO_8601
-
         :param str iso_string: An `ISO-8601` string. Learn more here: https://en.wikipedia.org/wiki/ISO_8601
         """
         self.iso_string = iso_string
@@ -25,27 +23,38 @@ def to_string(self) -> str:
         return self.iso_string
 
     def to_datetime_object(self) -> datetime:
+        iso_string = self._maybe_add_microseconds(self.iso_string)
         if self.has_timezone():
-            return datetime.strptime(self.iso_string, "%Y-%m-%dT%H:%M:%S.%fZ")
-        elif self.is_valid_iso_string_no_tz(self.iso_string):
-            return datetime.fromisoformat(self.iso_string)
+            return datetime.strptime(iso_string, "%Y-%m-%dT%H:%M:%S.%fZ")
+        else:
+            return datetime.fromisoformat(iso_string)
 
     def has_timezone(self) -> bool:
-        if self.is_valid_iso_string(self.iso_string):
-            return False if self.is_valid_iso_string_no_tz(self.iso_string) else True
+        if self.is_valid_iso_string_with_tz(self.iso_string):
+            return False if self.is_valid_iso_string_with_tz_no_tz(self.iso_string) else True
 
     @staticmethod
-    def is_valid_iso_string_no_tz(iso_str: str):
-        pattern = re.compile(RegexPatterns.VALID_ISO_STRING_NO_TZ.value)
+    def is_valid_iso_string_with_tz(iso_str: str):
+        pattern = re.compile(RegexPatterns.VALID_ISO_STRING.value)
         if pattern.match(iso_str):
             return True
         else:
             return False
 
     @staticmethod
-    def is_valid_iso_string(iso_str: str):
-        pattern = re.compile(RegexPatterns.VALID_ISO_STRING.value)
+    def is_valid_iso_string_with_tz_no_tz(iso_str: str):
+        pattern = re.compile(RegexPatterns.VALID_ISO_STRING_NO_TZ.value)
         if pattern.match(iso_str):
             return True
         else:
             return False
+
+    @staticmethod
+    def _maybe_add_microseconds(iso_str: str):
+        if "." not in iso_str:
+            if "Z" not in iso_str:
+                return iso_str + ".0"
+            else:
+                return iso_str[:-1] + ".0Z"
+        else:
+            return iso_str
diff --git a/shipengine_sdk/util/sdk_assertions.py b/shipengine_sdk/util/sdk_assertions.py
index ebe46c6..b45c2a0 100644
--- a/shipengine_sdk/util/sdk_assertions.py
+++ b/shipengine_sdk/util/sdk_assertions.py
@@ -174,8 +174,10 @@ def timeout_validation_error_assertions(error) -> None:
     assert error.source is ErrorSource.SHIPENGINE.value
 
 
-def is_response_404(status_code: int, response_body: Dict[str, Any], config) -> None:
-    """Check if status_code is 404 and raises an error if so."""
+def check_response_for_errors(status_code: int, response_body: Dict[str, Any], config) -> None:
+    """Checks response and status_code for 404, 429, and 500 error cases and raises an approved exception."""
+
+    # Check if status_code is 404 and raises an error if so.
     if "error" in response_body and status_code == 404:
         error = response_body["error"]
         error_data = error["data"]
@@ -194,12 +196,11 @@ def is_response_404(status_code: int, response_body: Dict[str, Any], config) ->
             error_code=ErrorCode.NOT_FOUND.value,
         )
 
-
-def is_response_429(status_code: int, response_body: Dict[str, Any], config) -> None:
-    """Check if status_code is 429 and raises an error if so."""
+    # Check if status_code is 429 and raises an error if so.
     if "error" in response_body and status_code == 429:
         error = response_body["error"]
-        retry_after = error["data"]["retryAfter"]
+        error_data = error["data"]
+        retry_after = error_data["details"]["retryAfter"]
         if retry_after > config.timeout:
             raise ClientTimeoutError(
                 retry_after=config.timeout,
@@ -213,9 +214,7 @@ def is_response_429(status_code: int, response_body: Dict[str, Any], config) ->
                 request_id=response_body["id"],
             )
 
-
-def is_response_500(status_code: int, response_body: Dict[str, Any]) -> None:
-    """Check if the status code is 500 and raises an error if so."""
+    # Check if the status code is 500 and raises an error if so.
     if status_code == 500:
         error = response_body["error"]
         error_data = error["data"]
diff --git a/tests/events/__init__.py b/tests/events/__init__.py
new file mode 100644
index 0000000..39fe0c3
--- /dev/null
+++ b/tests/events/__init__.py
@@ -0,0 +1 @@
+"""Tests around events emitted from ShipEngine SDK."""
diff --git a/tests/events/test_emitted_events.py b/tests/events/test_emitted_events.py
new file mode 100644
index 0000000..790ea0c
--- /dev/null
+++ b/tests/events/test_emitted_events.py
@@ -0,0 +1,238 @@
+"""Test that `RequestSentEvents` are emitted from the SDK properly."""
+from datetime import datetime
+
+from pytest_mock import MockerFixture
+
+from shipengine_sdk import __version__
+from shipengine_sdk.errors import (
+    ClientTimeoutError,
+    RateLimitExceededError,
+    ShipEngineError,
+)
+from shipengine_sdk.events import (
+    RequestSentEvent,
+    ResponseReceivedEvent,
+    ShipEngineEventListener,
+)
+from shipengine_sdk.models import ErrorCode, ErrorSource, ErrorType
+from shipengine_sdk.models.enums import Constants
+
+from ..util import (
+    assert_on_429_exception,
+    configurable_stub_shipengine_instance,
+    valid_residential_address,
+)
+
+
+class TestEmittedEvents:
+    def test_user_agent_includes_correct_sdk_version(self, mocker: MockerFixture) -> None:
+        """DX-1517 - Test user agent includes correct SDK version."""
+        request_sent_spy = mocker.spy(ShipEngineEventListener, "catch_request_sent_event")
+        config = {
+            "api_key": Constants.STUB_API_KEY.value,
+            "retries": 1,
+            "timeout": 10,
+        }
+        shipengine = configurable_stub_shipengine_instance(config=config)
+        shipengine.validate_address(address=valid_residential_address())
+        request_sent_return = request_sent_spy.spy_return
+        assert request_sent_return.headers["User-Agent"].split(" ")[0].split("/")[1] == __version__
+
+    def test_request_sent_event_on_retries(self, mocker: MockerFixture) -> None:
+        """DX-1521 - Test that a RequestSentEvent is emitted on retries."""
+        request_sent_spy = mocker.spy(ShipEngineEventListener, "catch_request_sent_event")
+        config = {
+            "api_key": Constants.STUB_API_KEY.value,
+            "retries": 1,
+            "timeout": 10,
+        }
+        shipengine = configurable_stub_shipengine_instance(config=config)
+        try:
+            shipengine.get_carrier_accounts(carrier_code="amazon_buy_shipping")
+        except ShipEngineError as err:
+            assert_on_429_exception(err=err, error_class=RateLimitExceededError)
+
+            request_sent_return = request_sent_spy.spy_return
+            assert request_sent_spy.call_count == 2
+            assert type(request_sent_return) == RequestSentEvent
+            assert request_sent_return.retry == 1
+            assert type(request_sent_return.timestamp) == datetime
+            assert request_sent_return.timeout == config["timeout"]
+            assert request_sent_return.body["method"] == "carrier.listAccounts.v1"
+            assert request_sent_return.base_uri == "https://api.shipengine.com/jsonrpc"
+            assert request_sent_return.headers["Api-Key"] == Constants.STUB_API_KEY.value
+            assert request_sent_return.headers["Content-Type"] == "application/json"
+            assert (
+                request_sent_return.message == "Retrying the ShipEngine carrier.listAccounts.v1 API"
+                " at https://api.shipengine.com/jsonrpc"
+            )
+
+    def test_response_received_event_success(self, mocker: MockerFixture) -> None:
+        """DX-1522 Test response received event success."""
+        test_start_time = datetime.now()
+        response_received_spy = mocker.spy(ShipEngineEventListener, "catch_response_received_event")
+        config = {
+            "api_key": Constants.STUB_API_KEY.value,
+            "retries": 2,
+            "timeout": 10,
+        }
+        shipengine = configurable_stub_shipengine_instance(config=config)
+        shipengine.validate_address(address=valid_residential_address())
+
+        response_recd_return = response_received_spy.spy_return
+        assert response_received_spy.call_count == 1
+        assert type(response_recd_return) == ResponseReceivedEvent
+        assert (
+            response_recd_return.message
+            == "Received an HTTP 200 response from the ShipEngine address.validate.v1 API"
+        )
+        assert response_recd_return.status_code == 200
+        assert response_recd_return.base_uri == "https://api.shipengine.com/jsonrpc"
+        assert response_recd_return.body["method"] == "address.validate.v1"
+        assert response_recd_return.retry == 0
+        assert response_recd_return.elapsed < test_start_time.second
+        assert response_recd_return.headers["Content-Type"].split(";")[0] == "application/json"
+
+    def test_response_received_on_error(self, mocker: MockerFixture) -> None:
+        """DX-1523 - Test response received event on error."""
+        test_start_time = datetime.now()
+        response_received_spy = mocker.spy(ShipEngineEventListener, "catch_response_received_event")
+        config = {
+            "api_key": Constants.STUB_API_KEY.value,
+            "retries": 1,
+            "timeout": 10,
+        }
+        shipengine = configurable_stub_shipengine_instance(config=config)
+        try:
+            shipengine.get_carrier_accounts(carrier_code="amazon_buy_shipping")
+        except ShipEngineError as err:
+            assert_on_429_exception(err=err, error_class=RateLimitExceededError)
+            response_recd_return = response_received_spy.spy_return
+            assert type(response_recd_return) == ResponseReceivedEvent
+            assert (
+                response_recd_return.message
+                == "Retrying the ShipEngine carrier.listAccounts.v1 API at https://api.shipengine.com/jsonrpc"
+            )
+            assert response_recd_return.status_code == 429
+            assert response_recd_return.base_uri == "https://api.shipengine.com/jsonrpc"
+            assert response_recd_return.body["method"] == "carrier.listAccounts.v1"
+            assert response_recd_return.retry == 1
+            assert response_recd_return.elapsed < test_start_time.second
+            assert (response_recd_return.timestamp - test_start_time).total_seconds() > 1
+
+    def test_config_with_retries_disabled(self, mocker: MockerFixture) -> None:
+        """DX-1527 - Tests that the SDK does not automatically retry if retries in config is set to 0."""
+        request_sent_spy = mocker.spy(ShipEngineEventListener, "catch_request_sent_event")
+        response_received_spy = mocker.spy(ShipEngineEventListener, "catch_response_received_event")
+        shipengine = configurable_stub_shipengine_instance(
+            {
+                "api_key": Constants.STUB_API_KEY.value,
+                "retries": 0,
+                "timeout": 10,
+            }
+        )
+        try:
+            shipengine.get_carrier_accounts(carrier_code="amazon_buy_shipping")
+        except ShipEngineError as err:
+            assert_on_429_exception(err=err, error_class=RateLimitExceededError)
+            request_sent_return = request_sent_spy.spy_return
+            assert request_sent_spy.call_count == 1
+            assert type(request_sent_return) == RequestSentEvent
+            assert request_sent_return.retry == 0
+
+            response_recd_return = response_received_spy.spy_return
+            assert request_sent_spy.call_count == 1
+            assert type(response_recd_return) == ResponseReceivedEvent
+            assert response_recd_return.retry == 0
+
+    def test_config_with_custom_retries(self, mocker: MockerFixture) -> None:
+        """DX-1528 - Test config with custom retries."""
+        request_sent_spy = mocker.spy(ShipEngineEventListener, "catch_request_sent_event")
+        response_received_spy = mocker.spy(ShipEngineEventListener, "catch_response_received_event")
+        shipengine = configurable_stub_shipengine_instance(
+            {
+                "api_key": Constants.STUB_API_KEY.value,
+                "retries": 3,
+                "timeout": 21,
+            }
+        )
+        try:
+            shipengine.get_carrier_accounts(carrier_code="amazon_buy_shipping")
+        except ShipEngineError as err:
+            assert_on_429_exception(err=err, error_class=RateLimitExceededError)
+            request_sent_return = request_sent_spy.spy_return
+            assert request_sent_spy.call_count == 4
+            assert type(request_sent_return) == RequestSentEvent
+            assert request_sent_return.retry == 3
+
+            response_recd_return = response_received_spy.spy_return
+            assert request_sent_spy.call_count == 4
+            assert type(response_recd_return) == ResponseReceivedEvent
+            assert response_recd_return.retry == 3
+
+    def test_timeout_err_when_retry_greater_than_timeout(self, mocker: MockerFixture) -> None:
+        """DX-1529 - Test timeout error when retry_after is greater than timeout."""
+        request_sent_spy = mocker.spy(ShipEngineEventListener, "catch_request_sent_event")
+        response_received_spy = mocker.spy(ShipEngineEventListener, "catch_response_received_event")
+        config = {
+            "api_key": Constants.STUB_API_KEY.value,
+            "retries": 3,
+            "timeout": 1,
+        }
+        shipengine = configurable_stub_shipengine_instance(config=config)
+        try:
+            shipengine.get_carrier_accounts(carrier_code="amazon_buy_shipping")
+        except ShipEngineError as err:
+            assert type(err) == ClientTimeoutError
+            assert err.request_id is not None
+            assert err.request_id.startswith("req_")
+            assert (
+                err.message
+                == f"The request took longer than the {config['timeout']} seconds allowed."
+            )
+            assert err.source is ErrorSource.SHIPENGINE.value
+            assert err.error_type is ErrorType.SYSTEM.value
+            assert err.error_code is ErrorCode.TIMEOUT.value
+            assert err.url == "https://www.shipengine.com/docs/rate-limits"
+
+            request_sent_return = request_sent_spy.spy_return
+            assert request_sent_spy.call_count == 1
+            assert type(request_sent_return) == RequestSentEvent
+            assert request_sent_return.retry == 0
+            assert request_sent_return.timeout == 1
+
+            response_recd_return = response_received_spy.spy_return
+            assert request_sent_spy.call_count == 1
+            assert type(response_recd_return) == ResponseReceivedEvent
+            assert response_recd_return.retry == 0
+
+    def test_retry_waits_correct_amount_of_time(self, mocker: MockerFixture) -> None:
+        """DX-1530 - retry waits the correct amount of time."""
+        test_start_time = datetime.now()
+        request_sent_spy = mocker.spy(ShipEngineEventListener, "catch_request_sent_event")
+        response_received_spy = mocker.spy(ShipEngineEventListener, "catch_response_received_event")
+        shipengine = configurable_stub_shipengine_instance(
+            {
+                "api_key": Constants.STUB_API_KEY.value,
+                "retries": 2,
+                "timeout": 10,
+            }
+        )
+        try:
+            shipengine.get_carrier_accounts(carrier_code="amazon_buy_shipping")
+        except ShipEngineError as err:
+            assert_on_429_exception(err=err, error_class=RateLimitExceededError)
+
+            request_sent_return = request_sent_spy.spy_return
+            assert request_sent_spy.call_count == 3
+            assert type(request_sent_return) == RequestSentEvent
+            assert request_sent_return.retry == 2
+            assert request_sent_return.timeout == 10
+
+            response_recd_return = response_received_spy.spy_return
+            assert request_sent_spy.call_count == 3
+            assert type(response_recd_return) == ResponseReceivedEvent
+            assert response_recd_return.retry == 2
+            assert (
+                int(str(round((test_start_time - datetime.now()).total_seconds())).strip("-")) <= 6
+            )
diff --git a/tests/http_client/test_http_client.py b/tests/http_client/test_http_client.py
index af6884a..b41776e 100644
--- a/tests/http_client/test_http_client.py
+++ b/tests/http_client/test_http_client.py
@@ -13,7 +13,6 @@ def validate_address(address):
     shipengine = ShipEngine(
         dict(
             api_key="baz",
-            base_uri=Endpoints.TEST_RPC_URL.value,
             page_size=50,
             retries=2,
             timeout=10,
@@ -47,7 +46,7 @@ class TestShipEngineClient:
     def test_500_server_response(self):
         responses.add(
             responses.POST,
-            Endpoints.TEST_RPC_URL.value,
+            Endpoints.SHIPENGINE_RPC_URL.value,
             json={
                 "jsonrpc": "2.0",
                 "id": "req_DezVNUvRkAP819f3JeqiuS",
@@ -74,7 +73,7 @@ def test_500_server_response(self):
     def test_404_server_response(self):
         responses.add(
             responses.POST,
-            Endpoints.TEST_RPC_URL.value,
+            Endpoints.SHIPENGINE_RPC_URL.value,
             json={
                 "jsonrpc": "2.0",
                 "id": "req_DezVNUvRkAP819f3JeqiuS",
diff --git a/tests/models/address/test_address.py b/tests/models/address/test_address.py
index 2c0856b..150c6f7 100644
--- a/tests/models/address/test_address.py
+++ b/tests/models/address/test_address.py
@@ -3,7 +3,7 @@
 
 from shipengine_sdk.errors import ValidationError
 from shipengine_sdk.models import ErrorCode, ErrorSource, ErrorType
-from tests.util.test_helpers import address_with_too_many_lines, empty_address_lines
+from tests.util import address_with_too_many_lines, empty_address_lines
 
 
 def address_line_assertions(err: ValidationError, variant: str) -> None:
diff --git a/tests/models/carriers/test_carrier_account.py b/tests/models/carriers/test_carrier_account.py
index d796aff..4fd8ab0 100644
--- a/tests/models/carriers/test_carrier_account.py
+++ b/tests/models/carriers/test_carrier_account.py
@@ -11,7 +11,7 @@ def stub_carrier_account_object() -> Dict[str, Any]:
     from the returned ShipEngine API response.
     """
     return {
-        "accountID": "car_1knseddGBrseWTiw",
+        "accountId": "car_1knseddGBrseWTiw",
         "accountNumber": "1169350",
         "carrierCode": "royal_mail",
         "name": "United Parcel Service",
diff --git a/tests/models/track_package/test_package.py b/tests/models/track_package/test_package.py
index abe4813..b21d5db 100644
--- a/tests/models/track_package/test_package.py
+++ b/tests/models/track_package/test_package.py
@@ -6,9 +6,9 @@
 
 def stub_package_data() -> Dict[str, Any]:
     return {
-        "packageID": "pkg_1FedExAccepted",
+        "packageId": "pkg_1FedExAccepted",
         "trackingNumber": "5fSkgyuh3GkfUjTZSEAQ8gHeTU29tZ",
-        "trackingURL": "https://www.fedex.com/track/5fSkgyuh3GkfUjTZSEAQ8gHeTU29tZ",
+        "trackingUrl": "https://www.fedex.com/track/5fSkgyuh3GkfUjTZSEAQ8gHeTU29tZ",
         "weight": {"value": 76, "unit": "kilogram"},
         "dimensions": {"length": 36, "width": 36, "height": 23, "unit": "inch"},
     }
diff --git a/tests/models/track_package/test_shipment.py b/tests/models/track_package/test_shipment.py
index 1c692b7..ba30ac7 100644
--- a/tests/models/track_package/test_shipment.py
+++ b/tests/models/track_package/test_shipment.py
@@ -5,6 +5,7 @@
 
 from shipengine_sdk.errors import ShipEngineError
 from shipengine_sdk.models import Shipment
+from shipengine_sdk.models.enums import Constants
 from shipengine_sdk.util.iso_string import IsoString
 
 from ...util import stub_shipengine_config
@@ -17,8 +18,8 @@ def stub_valid_shipment_data() -> Dict[str, Any]:
     """
     return {
         "carrierCode": "fedex",
-        "carrierAccountID": "car_kfUjTZSEAQ8gHeT",
-        "shipmentID": "shp_yuh3GkfUjTZSEAQ",
+        "carrierAccountId": Constants.CARRIER_ACCOUNT_ID_STUB.value,
+        "shipmentId": "shp_yuh3GkfUjTZSEAQ",
         "estimatedDelivery": "2021-06-15T21:00:00.000Z",
     }
 
@@ -26,18 +27,18 @@ def stub_valid_shipment_data() -> Dict[str, Any]:
 def stub_invalid_shipment_data() -> Dict[str, Any]:
     """
     Return a dictionary that mimics the Shipment data that would
-    be returned by ShipEngine API, where the `carrierAccountID` is invalid.
+    be returned by ShipEngine API, where the `carrierAccountId` is invalid.
     """
     return {
         "carrierCode": "fedex",
-        "carrierAccountID": "car_kfUoSHIPENGINEQ8gHeT",
-        "shipmentID": "shp_yuh3GkfUjTZSEAQ",
+        "carrierAccountId": "car_kfUoSHIPENGINEQ8gHeT",
+        "shipmentId": "shp_yuh3GkfUjTZSEAQ",
         "estimatedDelivery": "2021-06-15T21:00:00.000Z",
     }
 
 
 def stub_invalid_account_id_shipment_instantiation() -> Shipment:
-    """Return a test Shipment object that has an invalid `carrierAccountID`.."""
+    """Return a test Shipment object that has an invalid `carrierAccountId`.."""
     return Shipment(
         shipment=stub_invalid_shipment_data(),
         actual_delivery_date=IsoString("2021-06-10T21:00:00.000"),
diff --git a/tests/models/track_package/test_track_package_result.py b/tests/models/track_package/test_track_package_result.py
index c0612e9..f7541a0 100644
--- a/tests/models/track_package/test_track_package_result.py
+++ b/tests/models/track_package/test_track_package_result.py
@@ -2,6 +2,7 @@
 from typing import Any, Dict
 
 from shipengine_sdk.models import TrackingEvent, TrackPackageResult
+from shipengine_sdk.models.enums import Constants
 
 from ...util import stub_shipengine_config
 
@@ -17,14 +18,14 @@ def stub_track_package_data() -> Dict[str, Any]:
         "result": {
             "shipment": {
                 "carrierCode": "fedex",
-                "carrierAccountID": "car_kfUjTZSEAQ8gHeT",
-                "shipmentID": "shp_tJUaQJz3Twz57iL",
+                "carrierAccountId": Constants.CARRIER_ACCOUNT_ID_STUB.value,
+                "shipmentId": "shp_tJUaQJz3Twz57iL",
                 "estimatedDelivery": "2021-06-15T21:00:00.000Z",
             },
             "package": {
-                "packageID": "pkg_1FedexDeLiveredException",
+                "packageId": "pkg_1FedexDeLiveredException",
                 "trackingNumber": "2A4g3tJUaQJz3Twz57iLWBciD7wZWH",
-                "trackingURL": "https://www.fedex.com/track/2A4g3tJUaQJz3Twz57iLWBciD7wZWH",
+                "trackingUrl": "https://www.fedex.com/track/2A4g3tJUaQJz3Twz57iLWBciD7wZWH",
                 "weight": {"value": 76, "unit": "kilogram"},
                 "dimensions": {"length": 36, "width": 36, "height": 23, "unit": "inch"},
             },
diff --git a/tests/services/test_track_package.py b/tests/services/test_track_package.py
index d4e3a59..49fd566 100644
--- a/tests/services/test_track_package.py
+++ b/tests/services/test_track_package.py
@@ -23,11 +23,11 @@ def assertions_on_delivered_after_exception_or_multiple_attempts(
     assert len(tracking_result.events) == 8
     assert tracking_result.events[0].status == "accepted"
     assert tracking_result.events[1].status == "in_transit"
-    assert tracking_result.events[2].status == "unknown"
-    assert tracking_result.events[3].status == "in_transit"
+    assert tracking_result.events[2].status == "in_transit"
+    assert tracking_result.events[3].status == "unknown"
     assert tracking_result.events[4].status == "exception"
     assert tracking_result.events[5].status == "exception"
-    assert tracking_result.events[6].status == "in_transit"
+    assert tracking_result.events[6].status == "attempted_delivery"
     assert tracking_result.events[7].status == "delivered"
     assert tracking_result.events[-1].status == "delivered"
 
@@ -83,7 +83,7 @@ def test_track_by_tracking_number_and_carrier_code(self) -> None:
         tracking_data = TrackingQuery(carrier_code="fedex", tracking_number="abcFedExDelivered")
         tracking_result = shipengine.track_package(tracking_data=tracking_data)
 
-        assert tracking_data.carrier_code == tracking_result.shipment.carrier.code
+        assert tracking_data.carrier_code == tracking_result.shipment.carrier["code"]
         assert tracking_data.tracking_number == tracking_result.package.tracking_number
         assert tracking_result.package.tracking_url is not None
         assert type(tracking_result.package.tracking_url) is str
@@ -134,11 +134,7 @@ def test_multiple_delivery_attempts(self) -> None:
         assert tracking_result.events[1].status == "in_transit"
         assert tracking_result.events[2].status == "unknown"
         assert tracking_result.events[3].status == "in_transit"
-        assert tracking_result.events[4].status == "attempted_delivery"
-        assert tracking_result.events[5].status == "in_transit"
-        assert tracking_result.events[6].status == "attempted_delivery"
-        assert tracking_result.events[7].status == "in_transit"
-        assert tracking_result.events[8].status == "delivered"
+        assert tracking_result.events[-1].status == "delivered"
 
     def test_delivered_on_first_try(self) -> None:
         """DX-1091 - Test delivered on first try tracking event."""
@@ -171,7 +167,6 @@ def test_delivered_with_signature(self) -> None:
         assert len(tracking_result.events) == 5
         assert tracking_result.events[0].status == "accepted"
         assert tracking_result.events[1].status == "in_transit"
-        assert tracking_result.events[2].status == "unknown"
         assert tracking_result.events[3].status == "in_transit"
         assert tracking_result.events[4].status == "delivered"
         assert tracking_result.events[-1].status == "delivered"
@@ -229,11 +224,10 @@ def test_multiple_locations_in_tracking_event(self) -> None:
         track_package_assertions(tracking_result=tracking_result)
         assert_events_in_order(tracking_result.events)
         assert tracking_result.events[0].location is None
-        assert tracking_result.events[1].location is None
+        assert tracking_result.events[1].location.latitude is None
+        assert tracking_result.events[1].location.longitude is None
         assert type(tracking_result.events[2].location.latitude) is float
         assert type(tracking_result.events[2].location.longitude) is float
-        assert tracking_result.events[4].location.latitude is None
-        assert tracking_result.events[4].location.longitude is None
 
     def test_carrier_date_time_without_timezone(self) -> None:
         """DX-1098 - Test track package where carrierDateTime has no timezone."""
@@ -321,4 +315,4 @@ def test_server_side_error(self) -> None:
             assert err.source == ErrorSource.SHIPENGINE.value
             assert err.error_type == ErrorType.SYSTEM.value
             assert err.error_code == ErrorCode.UNSPECIFIED.value
-            assert err.message == "Unable to connect to the database"
+            assert err.message == "Unable to process this request. A downstream API error occurred."
diff --git a/tests/test_shipengine_config.py b/tests/test_shipengine_config.py
index 5357b74..81b392f 100644
--- a/tests/test_shipengine_config.py
+++ b/tests/test_shipengine_config.py
@@ -14,9 +14,7 @@ def stub_config() -> dict:
     Return a test configuration dictionary to be used
     when instantiating the ShipEngine object.
     """
-    return dict(
-        api_key="baz", base_uri=Endpoints.TEST_RPC_URL.value, page_size=50, retries=2, timeout=15
-    )
+    return dict(api_key="baz_sim", page_size=50, retries=2, timeout=15)
 
 
 def valid_residential_address() -> Address:
@@ -59,7 +57,7 @@ def set_config_timeout(timeout: int) -> ShipEngineConfig:
     :raises: :class:`InvalidFieldValueError`: If invalid value is passed into `ShipEngineConfig`
     object at instantiation.
     """
-    return ShipEngineConfig(dict(api_key="baz", timeout=timeout))
+    return ShipEngineConfig(dict(api_key="baz_sim", timeout=timeout))
 
 
 def set_config_retries(retries: int) -> ShipEngineConfig:
@@ -73,7 +71,7 @@ def set_config_retries(retries: int) -> ShipEngineConfig:
     :raises: :class:`InvalidFieldValueError`: If invalid value is passed into `ShipEngineConfig`
     object at instantiation.
     """
-    return ShipEngineConfig(dict(api_key="baz", retries=retries))
+    return ShipEngineConfig(dict(api_key="baz_sim", retries=retries))
 
 
 def complete_valid_config() -> ShipEngineConfig:
@@ -83,8 +81,7 @@ def complete_valid_config() -> ShipEngineConfig:
     """
     return ShipEngineConfig(
         dict(
-            api_key="baz",
-            base_uri=Endpoints.TEST_RPC_URL.value,
+            api_key="baz_sim",
             page_size=50,
             retries=2,
             timeout=10,
@@ -99,8 +96,8 @@ def test_valid_custom_config(self):
         valid values for each attribute.
         """
         valid_config: ShipEngineConfig = complete_valid_config()
-        assert valid_config.api_key == "baz"
-        assert valid_config.base_uri is Endpoints.TEST_RPC_URL.value
+        assert valid_config.api_key == "baz_sim"
+        assert valid_config.base_uri is Endpoints.SHIPENGINE_RPC_URL.value
         assert valid_config.page_size == 50
         assert valid_config.retries == 2
         assert valid_config.timeout == 10
@@ -127,7 +124,7 @@ def test_valid_retries(self):
         """Test case where a valid value is passed in for the retries."""
         retries = 2
         valid_retries = set_config_retries(retries)
-        assert valid_retries.api_key == "baz"
+        assert valid_retries.api_key == "baz_sim"
         assert valid_retries.retries == retries
 
     def test_invalid_retries_provided(self):
@@ -195,7 +192,7 @@ def test_invalid_api_key_in_method_call(self):
 
     def test_config_defaults(self) -> None:
         """Test default retries."""
-        config = ShipEngineConfig(dict(api_key="baz"))
+        config = ShipEngineConfig(dict(api_key="baz_sim"))
 
         assert config.retries == 1
         assert config.page_size == 50
diff --git a/tests/util/test_helpers.py b/tests/util/test_helpers.py
index 3eb7868..706155a 100644
--- a/tests/util/test_helpers.py
+++ b/tests/util/test_helpers.py
@@ -2,12 +2,16 @@
 from typing import Dict, Optional, Union
 
 from shipengine_sdk import ShipEngine, ShipEngineConfig
+from shipengine_sdk.errors import ShipEngineError
 from shipengine_sdk.models import (
     Address,
     AddressValidateResult,
-    Endpoints,
+    ErrorCode,
+    ErrorSource,
+    ErrorType,
     TrackingQuery,
 )
+from shipengine_sdk.models.enums import Constants
 
 
 def stub_config(
@@ -18,8 +22,7 @@ def stub_config(
     when instantiating the ShipEngine object.
     """
     return dict(
-        api_key="baz",
-        base_uri=Endpoints.TEST_RPC_URL.value,
+        api_key=Constants.STUB_API_KEY.value,
         page_size=50,
         retries=retries,
         timeout=15,
@@ -88,7 +91,7 @@ def address_with_warnings() -> Address:
     return Address(
         street=["170 Warning Blvd", "Apartment 32-B"],
         city_locality="Toronto",
-        state_province="ON",
+        state_province="On",
         postal_code="M6K 3C3",
         country_code="CA",
     )
@@ -121,7 +124,7 @@ def valid_canadian_address() -> Address:
     return Address(
         street=["170 Princes Blvd", "Ste 200"],
         city_locality="Toronto",
-        state_province="ON",
+        state_province="On",
         postal_code="M6K 3C3",
         country_code="CA",
     )
@@ -179,7 +182,7 @@ def unknown_address() -> Address:
     return Address(
         street=["4 Unknown St"],
         city_locality="Toronto",
-        state_province="ON",
+        state_province="On",
         postal_code="M6K 3C3",
         country_code="CA",
     )
@@ -240,6 +243,17 @@ def address_with_invalid_postal_code() -> Address:
     )
 
 
+def get_429_address() -> Address:
+    """Return an address that fetches a 429 fixture from the server."""
+    return Address(
+        street=["429 Rate Limit Error"],
+        city_locality="Boston",
+        state_province="MA",
+        postal_code="02215",
+        country_code="US",
+    )
+
+
 def get_server_side_error() -> Address:
     """Return an address that will cause the server to return a 500 server error."""
     return Address(
@@ -355,7 +369,7 @@ def canada_valid_avs_assertions(
     assert address is not None
     assert address.city_locality == original_address.city_locality
     assert address.state_province == original_address.state_province.title()
-    assert address.postal_code == "M6 K 3 C3"
+    assert address.postal_code == "M6K 3C3"
     assert address.country_code == original_address.country_code.upper()
     assert address.is_residential is expected_residential_indicator
 
@@ -389,6 +403,19 @@ def canada_valid_normalize_assertions(
     assert type(normalized_address) is Address
     assert normalized_address.city_locality == original_address.city_locality
     assert normalized_address.state_province == original_address.state_province.title()
-    assert normalized_address.postal_code == "M6 K 3 C3"
+    assert normalized_address.postal_code == "M6K 3C3"
     assert normalized_address.country_code == original_address.country_code.upper()
     assert normalized_address.is_residential is expected_residential_indicator
+
+
+def assert_on_429_exception(err: ShipEngineError, error_class: object) -> None:
+    error = err.to_dict()
+    assert type(err) == error_class
+    assert error["request_id"] is not None
+    assert error["request_id"].startswith("req_")
+    assert error["source"] is ErrorSource.SHIPENGINE.value
+    assert error["error_type"] is ErrorType.SYSTEM.value
+    assert error["error_code"] is ErrorCode.RATE_LIMIT_EXCEEDED.value
+    assert error["message"] == "You have exceeded the rate limit."
+    assert error["url"] is not None
+    assert error["url"] == "https://www.shipengine.com/docs/rate-limits"
diff --git a/tests/util/test_iso_string.py b/tests/util/test_iso_string.py
index 63a723f..b204828 100644
--- a/tests/util/test_iso_string.py
+++ b/tests/util/test_iso_string.py
@@ -9,19 +9,14 @@ class TestIsoString:
 
     def test_to_string(self) -> None:
         iso_str = IsoString(self._test_iso_string_no_tz).to_string()
-
         assert type(iso_str) is str
 
     def test_to_datetime_object(self) -> None:
         iso_str = IsoString(self._test_iso_string_no_tz).to_datetime_object()
-
         assert type(iso_str) is datetime.datetime
 
-    def test_static_no_tz_check(self) -> None:
-        assert IsoString.is_valid_iso_string_no_tz(self._test_iso_string_no_tz) is True
-
     def test_static_valid_iso_check(self) -> None:
-        assert IsoString.is_valid_iso_string(self._test_iso_string_no_tz) is True
+        assert IsoString.is_valid_iso_string_with_tz(self._test_iso_string_no_tz) is True
 
     def test_static_valid_iso_check_failure(self) -> None:
-        assert IsoString.is_valid_iso_string("2021-06-10T21:00:00.000K") is False
+        assert IsoString.is_valid_iso_string_with_tz("2021-06-10T21:00:00.000K") is False
diff --git a/tox.ini b/tox.ini
index 114a92e..f69bfac 100644
--- a/tox.ini
+++ b/tox.ini
@@ -30,10 +30,12 @@ changedir = tests
 deps =
     pytest
     pytest-cov
+    pytest-mock
     flake8
     coverage
     coveralls
     responses
+    fuuid
 commands =
     pytest {posargs:}
 ;    coveralls --submit={toxworkdir}/.coverage.{envname}