diff --git a/python/activator/activator.py b/python/activator/activator.py
index a080a429..f6488b43 100644
--- a/python/activator/activator.py
+++ b/python/activator/activator.py
@@ -1,3 +1,26 @@
+# This file is part of prompt_prototype.
+#
+# Developed for the LSST Data Management System.
+# This product includes software developed by the LSST Project
+# (https://www.lsst.org).
+# See the COPYRIGHT file at the top-level directory of this distribution
+# for details of code ownership.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+__all__ = ["check_for_snap", "next_visit_handler"]
+
 import base64
 import json
 import logging
@@ -9,8 +32,8 @@
 from flask import Flask, request
 from google.cloud import pubsub_v1, storage
 
-from middleware_interface import MiddlewareInterface
-from visit import Visit
+from .middleware_interface import MiddlewareInterface
+from .visit import Visit
 
 PROJECT_ID = "prompt-proto"
 
diff --git a/python/activator/middleware_interface.py b/python/activator/middleware_interface.py
index 94de4913..c995ab83 100644
--- a/python/activator/middleware_interface.py
+++ b/python/activator/middleware_interface.py
@@ -1,3 +1,26 @@
+# This file is part of prompt_prototype.
+#
+# Developed for the LSST Data Management System.
+# This product includes software developed by the LSST Project
+# (https://www.lsst.org).
+# See the COPYRIGHT file at the top-level directory of this distribution
+# for details of code ownership.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+__all__ = ["MiddlewareInterface"]
+
 import logging
 import os
 import shutil
@@ -5,7 +28,7 @@
 from astropy.time import Time
 from lsst.daf.butler import Butler
 
-from visit import Visit
+from .visit import Visit
 
 PIPELINE_MAP = dict(
     BIAS="bias.yaml",
@@ -18,6 +41,26 @@
 
 
 class MiddlewareInterface:
+    """Interface layer between the Butler middleware and the prompt processing
+    data handling system.
+
+    An instance of this class will accept an incoming group of snaps to
+    process, using an instance-local butler repo. The instance can pre-load
+    the necessary calibrations to process an incoming visit, ingest the data
+    when it is available, and run the difference imaging pipeline, all in that
+    local butler.
+
+    Parameters
+    ----------
+    input_repo : `str`
+        Path to a butler repo containing the calibration and other data needed
+        for processing images as they are received.
+    image_bucket : `str`
+        Google storage bucket where images will be written to as they arrive.
+    instrument : `str`
+        Name of the instrument taking the data, for populating butler
+        collections and dataIds.
+    """
     def __init__(self, input_repo: str, image_bucket: str, instrument: str):
 
         # self.src = Butler(input_repo, writeable=False)
@@ -25,7 +68,7 @@ def __init__(self, input_repo: str, image_bucket: str, instrument: str):
         self.image_bucket = image_bucket
         self.instrument = instrument
 
-        self.repo = "/tmp/butler-{os.getpid()}"
+        self.repo = f"/tmp/butler-{os.getpid()}"
         if not os.path.exists(self.repo):
             _log.info(f"Making local Butler {self.repo}")
             Butler.makeRepo(self.repo)
@@ -83,6 +126,13 @@ def __init__(self, input_repo: str, image_bucket: str, instrument: str):
         self.calib_types = ["bias", "dark", "defects", "flat", "fringe", ]
 
     def prep_butler(self, visit: Visit) -> None:
+        """Prepare a temporary butler repo for processing the incoming data.
+
+        Parameters
+        ----------
+        visit : Visit
+            Group of snaps from one detector to prepare the butler for.
+        """
         _log.info(f"Preparing Butler for visit '{visit}'")
         visit_info = visit.__dict__
         for calib_type in self.calib_types:
@@ -122,6 +172,14 @@ def prep_butler(self, visit: Visit) -> None:
         shutil.rmtree(visit_dir, ignore_errors=True)
 
     def ingest_image(self, oid: str) -> None:
+        """Ingest an image into the temporary butler.
+
+        Parameters
+        ----------
+        oid : `str`
+            Google storage identifier for incoming image, relative to the
+            image bucket.
+        """
         _log.info(f"Ingesting image '{oid}'")
         run = f"{self.instrument}/raw/all"
         cmd = [
@@ -137,7 +195,19 @@ def ingest_image(self, oid: str) -> None:
         _log.debug(str(cmd))
         # subprocess.run(cmd, check=True)
 
-    def run_pipeline(self, visit: Visit, snaps) -> None:
+    def run_pipeline(self, visit: Visit, snaps: set) -> None:
+        """Process the received image.
+
+        Parameters
+        ----------
+        visit : Visit
+            Group of snaps from one detector to be processed.
+        snaps : `set`
+            Identifiers of the snaps that were received.
+            TODO: I believe this is unnecessary because it should be encoded
+            in the `visit` object, but we'll have to test how that works once
+            we implemented this with actual data.
+        """
         pipeline = PIPELINE_MAP[visit.kind]
         _log.info(f"Running pipeline {pipeline} on visit '{visit}', snaps {snaps}")
         cmd = [
diff --git a/python/activator/visit.py b/python/activator/visit.py
index b28fac99..b2729ac7 100644
--- a/python/activator/visit.py
+++ b/python/activator/visit.py
@@ -1,3 +1,5 @@
+__all__ = ["Visit"]
+
 from dataclasses import dataclass
 
 
diff --git a/python/tester/upload.py b/python/tester/upload.py
index a15680d8..607a23af 100644
--- a/python/tester/upload.py
+++ b/python/tester/upload.py
@@ -44,7 +44,7 @@ def process_group(publisher, bucket, instrument, group, filter, kind):
         logging.info(f"Taking group {group} snap {snap}")
         time.sleep(EXPOSURE_INTERVAL)
         for detector in range(INSTRUMENTS[instrument].n_detectors):
-            logging.info(f"Uploading {group} {snap} {filter} {detector}")
+            logging.info(f"Uploading group: {group} snap: {snap} filter: {filter} detector: {detector}")
             exposure_id = (group // 100000) * 100000
             exposure_id += (group % 100000) * INSTRUMENTS[instrument].n_snaps
             exposure_id += snap
diff --git a/tests/test_middleware_interface.py b/tests/test_middleware_interface.py
new file mode 100644
index 00000000..4463012b
--- /dev/null
+++ b/tests/test_middleware_interface.py
@@ -0,0 +1,72 @@
+# This file is part of prompt_prototype.
+#
+# Developed for the LSST Data Management System.
+# This product includes software developed by the LSST Project
+# (https://www.lsst.org).
+# See the COPYRIGHT file at the top-level directory of this distribution
+# for details of code ownership.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+import os.path
+import tempfile
+import unittest
+
+from activator.middleware_interface import MiddlewareInterface
+from activator.visit import Visit
+
+
+class MiddlewareInterfaceTest(unittest.TestCase):
+    def setUp(self):
+        input_dir = os.path.join(os.path.abspath(os.path.dirname(__file__)), "data")
+        instrument = "TestCam"
+        self.output_dir = tempfile.TemporaryDirectory()
+        self.interface = MiddlewareInterface(input_dir, self.output_dir, instrument)
+        self.next_visit = Visit(instrument,
+                                detector=1,
+                                group=1,
+                                snaps=1,
+                                filter="r",
+                                ra=10,
+                                dec=20,
+                                kind="BIAS")
+        self.logger_name = "activator.middleware_interface"
+
+    def test_init(self):
+        """Basic tests of initializing an interface object.
+        """
+        # did we get a useable butler instance?
+        self.assertIn("/tmp/butler-", self.interface.dest.datastore.root.path)
+        # Ideas for things to test:
+        # * On init, does the right kind of butler get created, with the right
+        #   collections, etc?
+        # * On init, is the local butler repo purely in memory?
+
+    def test_prep_butler(self):
+        with self.assertLogs(self.logger_name, level="INFO") as cm:
+            self.interface.prep_butler(self.next_visit)
+        msg = f"INFO:{self.logger_name}:Preparing Butler for visit '{self.next_visit}'"
+        self.assertEqual(cm.output, [msg])
+
+    def test_ingest_image(self):
+        with self.assertLogs(self.logger_name, level="INFO") as cm:
+            self.interface.ingest_image(self.next_visit)
+        msg = f"INFO:{self.logger_name}:Ingesting image '{self.next_visit}'"
+        self.assertEqual(cm.output, [msg])
+
+    def test_run_pipeline(self):
+        with self.assertLogs(self.logger_name, level="INFO") as cm:
+            self.interface.run_pipeline(self.next_visit, 1)
+        msg = f"INFO:{self.logger_name}:Running pipeline bias.yaml on visit '{self.next_visit}', snaps 1"
+        self.assertEqual(cm.output, [msg])