Add a CI workflow running py_compile and the test suite

.github/workflows/tests.yml

@@ -0,0 +1,37 @@
+name: Tests
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        # the declared floor in README.md, and a current release
+        python-version: ["3.8", "3.13"]
+    steps:
+      - uses: actions/checkout@v5
+
+      - uses: actions/setup-python@v6
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Compile both modules
+        run: python -m py_compile src/collide.py src/ideaCollisionGenerator.py
+
+      - name: Run the test suite
+        run: python -m unittest discover -s tests -v
+
+      # the suite patches every prompt, so the real stdin path documented in
+      # README.md is exercised here instead
+      - name: Run the program end to end
+        run: |
+          printf 'k%s\n' 1 2 3 4 5 6 7 8 9 10 > fixture.txt
+          printf 'idea %s\n' 1 2 3 4 5 >> fixture.txt
+          python src/collide.py < fixture.txt
+          written=$(cat ideas/ideas-*.txt | wc -l)
+          test "$written" -eq 5

README.md

@@ -74,6 +74,11 @@ python3 -m unittest discover -s tests
 
 Every prompt is patched, so no test waits on real input.
 
+[`.github/workflows/tests.yml`](.github/workflows/tests.yml) runs the same
+commands on every push to `main` and on every pull request, against Python 3.8
+and 3.13: `py_compile` over both modules, the test suite, and one full run of
+the program with a 15-line fixture on stdin.
+
 ## License
 
 See [LICENSE](LICENSE).