Run the unit test suite in GitHub Actions

.github/workflows/tests.yml

@@ -0,0 +1,33 @@
+name: Tests
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      # The Viron submodule is deliberately not checked out: the test suite stubs it in
+      # sys.modules, and only main.py needs it at runtime.
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      # render_window.py imports pygame, and tests/test_headless_run.py drives the real
+      # pygame with SDL's dummy drivers, so it has to be installed even though most tests mock it.
+      - name: Install dependencies
+        run: python -m pip install pygame
+
+      - name: Check syntax
+        run: python -m py_compile main.py graphik.py __init__.py render_window.py headless_run.py usage_reporting.py trace_client.py
+
+      - name: Run unit tests
+        run: python -m unittest discover -s tests

README.md

@@ -170,6 +170,8 @@ python -m unittest discover -s tests
 
 Run the command from the repository root, so that `main.py` and `render_window.py` are importable.
 
+The same command, preceded by a `py_compile` syntax check of the top-level modules, is run by the `Tests` GitHub Actions workflow (`.github/workflows/tests.yml`) on every pull request targeting `main` and on every push to `main`. The workflow checks the repository out without the `Viron` submodule, since the suite does not need it.
+
 ### Running without Docker or a display
 
 `headless_run.py` drives `main()` end to end when neither a Viron server nor a display is available. The real Pygame, `RenderWindow` and `Graphik` are used, rendering to SDL's `dummy` video and audio drivers (unless `SDL_VIDEODRIVER` or `SDL_AUDIODRIVER` is already set); only Viron is replaced, by in-memory services with one location per grid cell. Like the test suite, it needs neither the `Viron/` submodule nor Python 3.10+.