diff --git a/.circleci/config.yml b/.circleci/config.yml
index 90cb547..6ecc9ae 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -13,6 +13,12 @@ jobs:
             . venv/bin/activate
             pip install --requirement dev_requirements.txt
             ./dev-scripts/build
+      - run:
+          name: install coveralls and upload coverage information
+          command: |
+            . venv/bin/activate
+            pip install coveralls==3.0.1
+            coveralls
   install:
     docker:
       - image: circleci/python:3.7.3
diff --git a/README.md b/README.md
index 9b17ed6..28a6243 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # pyrestic
 
-[![CircleCI](https://circleci.com/gh/mtlynch/pyrestic.svg?style=svg)](https://circleci.com/gh/mtlynch/pyrestic) [![License](http://img.shields.io/:license-mit-blue.svg?style=flat-square)](LICENSE)
+[![CircleCI](https://circleci.com/gh/mtlynch/pyrestic.svg?style=svg)](https://circleci.com/gh/mtlynch/pyrestic) [![Coverage Status](https://coveralls.io/repos/github/mtlynch/pyrestic/badge.svg?branch=master)](https://coveralls.io/github/mtlynch/pyrestic?branch=master) [![License](http://img.shields.io/:license-mit-blue.svg?style=flat-square)](LICENSE)
 
 ## Overview
 
diff --git a/dev-scripts/build b/dev-scripts/build
index b13f5a1..59569ed 100755
--- a/dev-scripts/build
+++ b/dev-scripts/build
@@ -22,6 +22,13 @@ find . \
   -not -path "./${VIRTUALENV_DIR}/*" \
   -delete
 
+# Run unit tests and calculate code coverage.
+coverage run \
+  --source "$SOURCE_DIR" \
+  --omit "*_test.py" \
+  -m unittest discover --pattern "*_test.py"
+coverage report
+
 # Check that source has correct formatting.
 yapf \
   --diff \
diff --git a/dev_requirements.txt b/dev_requirements.txt
index 631f5ad..6051c6f 100644
--- a/dev_requirements.txt
+++ b/dev_requirements.txt
@@ -1,3 +1,4 @@
+coverage==5.5
 isort[requirements_deprecated_finder]==5.7.0
 pyflakes==2.2.0
 yapf==0.31.0
diff --git a/restic/__init__.py b/restic/__init__.py
new file mode 100644
index 0000000..bfb5871
--- /dev/null
+++ b/restic/__init__.py
@@ -0,0 +1,10 @@
+from restic.internal import self_update as internal_self_update
+from restic.internal import version as internal_version
+
+
+def self_update():
+    return internal_self_update.run()
+
+
+def version():
+    return internal_version.run()
diff --git a/restic/core.py b/restic/core.py
deleted file mode 100644
index e6bc37d..0000000
--- a/restic/core.py
+++ /dev/null
@@ -1,86 +0,0 @@
-import re
-import subprocess
-
-from restic.config import restic_bin
-
-
-def run_restic(cmd):
-    out = ''
-    err = ''
-    try:
-        with subprocess.Popen(cmd,
-                              stdin=subprocess.PIPE,
-                              stdout=subprocess.PIPE,
-                              encoding='utf-8',
-                              text=True) as proc:
-            out, err = proc.communicate()
-            if err is not None:
-                raise RuntimeError('Command runtime failure')
-            proc.wait()
-            if proc.returncode != 0:
-                raise RuntimeError(f'Return code {proc.returncode} is not zero')
-    except FileNotFoundError:
-        raise RuntimeError('Cannot find restic installed')
-
-    return out
-
-
-def version():
-    cmd = [restic_bin, 'version']
-    out = run_restic(cmd)
-    if out is None:
-        return None
-    matchObj = re.match(
-        r'restic ([0-9\.]+) compiled with go([0-9\.]+) on ([a-zA-Z0-9]+)/([a-zA-Z0-9]+)',
-        out)
-    return {
-        'restic_version': matchObj.group(1),
-        'go_version': matchObj.group(2),
-        'platform_version': matchObj.group(3),
-        'Architecture': matchObj.group(4)
-    }
-
-
-def self_update():
-    cmd = [restic_bin, 'self-update']
-    run_restic(cmd)
-
-
-def generate(bash_completion=None, man=None, zsh_completion=None):
-    cmd = [restic_bin, 'generate']
-    if bash_completion is not None:
-        if type(bash_completion) == str:
-            cmd.extend(['--bash-completion', bash_completion])
-        else:
-            raise ValueError('bash-completion shall be type of str or None')
-
-    if man is not None:
-        if type(man) == str:
-            cmd.extend(['--man', man])
-        else:
-            raise ValueError('man shall be type of str or None')
-
-    if zsh_completion is not None:
-        if type(zsh_completion) == str:
-            cmd.extend(['--zsh-completion', zsh_completion])
-        else:
-            raise ValueError('zsh-completion shall be type of str or None')
-
-    run_restic(cmd)
-
-
-'''
-TODO: if there is a repository, it needs pasword.
-'''
-
-
-def is_initialized(path):
-    cmd = ['restic', '-r', path, 'snapshots']
-    ret = run_restic(cmd)
-    lines = ret.splitlines()
-    for each_line in lines:
-        if each_line.strip(
-        ) == 'Is there a repository at the following location?':
-            return False
-
-    return True
diff --git a/restic/generate.py b/restic/generate.py
new file mode 100644
index 0000000..2dbeda9
--- /dev/null
+++ b/restic/generate.py
@@ -0,0 +1,25 @@
+from restic.config import restic_bin
+from restic.internal import command_executor
+
+
+def generate(bash_completion=None, man=None, zsh_completion=None):
+    cmd = [restic_bin, 'generate']
+    if bash_completion is not None:
+        if type(bash_completion) == str:
+            cmd.extend(['--bash-completion', bash_completion])
+        else:
+            raise ValueError('bash-completion shall be type of str or None')
+
+    if man is not None:
+        if type(man) == str:
+            cmd.extend(['--man', man])
+        else:
+            raise ValueError('man shall be type of str or None')
+
+    if zsh_completion is not None:
+        if type(zsh_completion) == str:
+            cmd.extend(['--zsh-completion', zsh_completion])
+        else:
+            raise ValueError('zsh-completion shall be type of str or None')
+
+    command_executor.execute(cmd)
diff --git a/restic/internal/__init__.py b/restic/internal/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/restic/internal/command_executor.py b/restic/internal/command_executor.py
new file mode 100644
index 0000000..60b95a3
--- /dev/null
+++ b/restic/internal/command_executor.py
@@ -0,0 +1,22 @@
+import subprocess
+
+
+def execute(cmd):
+    out = ''
+    err = ''
+    try:
+        with subprocess.Popen(cmd,
+                              stdin=subprocess.PIPE,
+                              stdout=subprocess.PIPE,
+                              encoding='utf-8',
+                              text=True) as proc:
+            out, err = proc.communicate()
+            if err is not None:
+                raise RuntimeError('Command runtime failure')
+            proc.wait()
+            if proc.returncode != 0:
+                raise RuntimeError(f'Return code {proc.returncode} is not zero')
+    except FileNotFoundError:
+        raise RuntimeError('Cannot find restic installed')
+
+    return out
diff --git a/restic/internal/self_update.py b/restic/internal/self_update.py
new file mode 100644
index 0000000..6cfba36
--- /dev/null
+++ b/restic/internal/self_update.py
@@ -0,0 +1,7 @@
+from restic.config import restic_bin
+from restic.internal import command_executor
+
+
+def run():
+    cmd = [restic_bin, 'self-update']
+    command_executor.execute(cmd)
diff --git a/restic/internal/self_update_test.py b/restic/internal/self_update_test.py
new file mode 100644
index 0000000..e5f7ca3
--- /dev/null
+++ b/restic/internal/self_update_test.py
@@ -0,0 +1,13 @@
+import unittest
+from unittest import mock
+
+import restic
+from restic.internal import self_update
+
+
+class SelfUpdateTest(unittest.TestCase):
+
+    @mock.patch.object(self_update.command_executor, 'execute')
+    def test_self_update(self, mock_execute):
+        restic.self_update()
+        mock_execute.assert_called_with(['restic', 'self-update'])
diff --git a/restic/internal/version.py b/restic/internal/version.py
new file mode 100644
index 0000000..f95d580
--- /dev/null
+++ b/restic/internal/version.py
@@ -0,0 +1,18 @@
+import re
+
+from restic import config
+from restic.internal import command_executor
+
+
+def run():
+    cmd = [config.restic_bin, 'version']
+    out = command_executor.execute(cmd)
+    match = re.match(
+        r'restic ([0-9\.]+) compiled with go([0-9\.]+) on ([a-zA-Z0-9]+)/([a-zA-Z0-9]+)',
+        out)
+    return {
+        'restic_version': match.group(1),
+        'go_version': match.group(2),
+        'platform_version': match.group(3),
+        'architecture': match.group(4)
+    }
diff --git a/restic/internal/version_test.py b/restic/internal/version_test.py
new file mode 100644
index 0000000..6d578b5
--- /dev/null
+++ b/restic/internal/version_test.py
@@ -0,0 +1,23 @@
+import unittest
+from unittest import mock
+
+import restic
+from restic.internal import version
+
+
+class VersionTest(unittest.TestCase):
+
+    @mock.patch.object(version.command_executor, 'execute')
+    def test_version(self, mock_execute):
+        mock_execute.return_value = (
+            'restic 0.12.0 compiled with go1.15.8 on windows/amd64')
+
+        self.assertEqual(
+            {
+                'architecture': 'amd64',
+                'go_version': '1.15.8',
+                'platform_version': 'windows',
+                'restic_version': '0.12.0'
+            }, restic.version())
+
+        mock_execute.assert_called_with(['restic', 'version'])