Add module level docstrings.

tests/test_dummy_server.py

@@ -1,3 +1,13 @@
+"""Test the server without creating a full HTTP server and socket connection.
+
+Rather than spinning up a full uvicorn webserver for each test these tests use
+the FastAPI ``TestClient`` or to directly communicate with the underlying
+LabThings-FastAPI code. This increases speed of testing significantly.
+
+For tests that require a full running server see the ``integration-tests``
+directory in the root of the repository.
+"""
+
 import json
 import os
 import tempfile

tests/test_scan_directories.py

@@ -1,3 +1,5 @@
+"""Test the functionality in the scan_directories module."""
+
 import tempfile
 import os
 import math

tests/test_scan_planners.py

@@ -1,3 +1,9 @@
+"""Test the scan planning algorithms of the Microscope.
+
+As well as low level function by function tests, this test suite also provides tests
+that simulate scanning a sample, checking that the expected path is followed.
+"""
+
 import pytest
 from copy import copy
 

tests/utilities/scan_test_helpers.py

@@ -1,3 +1,9 @@
+"""Utility functions for testing scan planners.
+
+These including fake sample creation, scan path visualisation, and
+persistent storage of expected scan paths for samples.
+"""
+
 import os
 import pickle