Bug 1621728: Added a guide for writing tests

docs/testing.md

@@ -116,4 +116,8 @@ There are a lot of taskid, revisions, and expected fields to update in tests.  F
 - ensure variety of platforms, builds, tests, pass/fail, etc. are included
 - push_data.json - adjust the dates to have multiple days (1st +1, 2nd +2, 3rd +3)
 
+## Writing Tests
+
+For guidance on writing tests (conventions, examples, and recommended frameworks), see the separate guide: [Writing Tests](writing_tests.md).
+
 [eslint]: https://eslint.org

docs/writing_tests.md

@@ -0,0 +1,67 @@
+# Writing Tests
+
+## Purpose
+
+- Tests should be fast, deterministic, and focused. Prefer unit tests for logic, integration tests for component interactions, and end-to-end tests for critical workflows.
+
+## Frameworks we use
+
+- Python
+  - Test runner: `pytest` (with `pytest-django` for Django integration).
+  - Mocks: `responses` for HTTP responses; `pytest-mock` patterns also appear.
+  - Test data: fixtures under `tests/sample_data/`.
+  - Database tests: use `@pytest.mark.django_db`.
+- Frontend
+  - Unit tests: `Jest` with React Testing Library.
+  - Integration: PollyJS recordings are used for integration tests to record/replay API interactions.
+  - End-to-end: `jest-puppeteer`/Puppeteer is available for e2e tests.
+
+## Guidelines
+
+- Test small units of logic first (pure functions, transformers).
+- Use `responses` to mock external HTTP requests.
+- Use `@pytest.mark.django_db` when interacting with the DB.
+- Keep unit tests fast (<100ms each ideally). Group slow tests and run separately.
+- For frontend components use React Testing Library; avoid testing implementation details.
+- Use fixtures (`tests/conftest.py`) and shared sample data in `tests/sample_data/`.
+- Freeze time where necessary or inject clock values (e.g., `freezegun`) to keep tests deterministic.
+
+## Examples
+
+- Mocking HTTP:
+
+```python
+responses.add(responses.GET, "https://api.example", json={"ok": True}, status=200)
+```
+
+- Simple pytest fixture:
+
+```python
+@pytest.fixture
+def github_push(sample_data):
+    return copy.deepcopy(sample_data.github_push)
+```
+
+- DB test example:
+
+```python
+@pytest.mark.django_db
+def test_ingest_hg_push(...):
+    PushLoader().process(...)
+    assert Push.objects.count() == 1
+```
+
+## Resources
+
+- [Pytest](https://docs.pytest.org/)
+- [Pytest-Django](https://pytest-django.readthedocs.io/)
+- [Responses](https://github.com/getsentry/responses)
+- [React Testing Library](https://testing-library.com/)
+- [Jest](https://jestjs.io/)
+- [PollyJS](https://netflix.github.io/pollyjs/)
+
+## Best practices
+
+- Keep tests deterministic and mock external dependencies.
+- Run `yarn test` and `pytest` locally in Docker as per `docs/testing.md`.
+- Add tests for bug fixes and new public APIs.

mkdocs.yml

@@ -34,7 +34,9 @@ nav:
   - About: 'index.md'
   - Development:
       - Installation: 'installation.md'
-      - Testing: 'testing.md'
+      - Testing:
+          - Testing: 'testing.md'
+          - Writing Tests: 'writing_tests.md'
       - Loading Pulse data: 'pulseload.md'
       - Code Style: 'code_style.md'
       - Accessibility: 'accessibility.md'