testing

name	testing
description	Write comprehensive, maintainable tests following TDD and AAA pattern. Use when writing unit tests, integration tests, setting up fixtures, mocking dependencies, or improving test coverage. Covers Python (pytest) and Swift (Swift Testing framework). Do NOT use for mutation testing specifics.
metadata	{"author":"Geoff","version":"1.0.0"}

Testing

Test behavior, not implementation. One assertion concept per test. Follow AAA (Arrange-Act-Assert).

Instructions

Step 1: Follow the Principles

1. Test behavior, not implementation
2. One assertion concept per test
3. Follow AAA pattern (Arrange-Act-Assert)
4. Write tests first (TDD) when possible
5. Keep tests fast and isolated
6. Make tests readable and self-documenting

Step 2: Apply Language-Specific Patterns

Python (pytest):

• Use pytest classes to group related tests
• Use fixtures for setup/teardown
• Use @pytest.mark.parametrize for data-driven tests
• Use httpx.AsyncClient for FastAPI endpoint tests
• Mock external dependencies, not internal logic

Swift (Swift Testing):

• Use @Test attribute (not XCTest)
• Use #expect() for assertions (not XCTAssert)
• Use @Suite to group related tests
• Use descriptive test function names: func featureName_scenario_expectedResult()
• Keep test files in WavelengthWatch Watch AppTests/

Step 3: Follow Coverage Best Practices

• Test edge cases: empty inputs, boundary values, nil, concurrent access
• Test error paths, not just happy paths
• Don't test third-party code - mock external services
• Backend: pytest --cov=backend --cov-report=html
• Frontend: test via run-tests-individually.sh

Examples

Example 1: Python Unit Test with Parametrize

class TestJournalValidation:
    def test_valid_entry_creates_successfully(self, db_session):
        entry = create_journal_entry(feeling_id=1, strategy_id=1)
        assert entry.id is not None
        assert entry.feeling_id == 1

    @pytest.mark.parametrize("feeling_id,expected_error", [
        (None, "feeling_id is required"),
        (999, "feeling not found"),
    ])
    def test_invalid_feeling_raises_error(self, db_session, feeling_id, expected_error):
        with pytest.raises(ValueError, match=expected_error):
            create_journal_entry(feeling_id=feeling_id)

Example 2: Swift Testing

@Suite struct WLColorTokensTests {
    @Test func namedLayerColors_allElevenAreDefined() {
        let colors = [
            WLColorTokens.beige, WLColorTokens.purple, WLColorTokens.red,
            WLColorTokens.blue, WLColorTokens.orange, WLColorTokens.green,
        ]
        #expect(colors.count == 6)
    }

    @Test func layerColor_returnsNonNilForValidStage() {
        let color = WLColorTokens.layer("Beige")
        #expect(color != nil)
    }
}

Troubleshooting

Error: Tests are slow

• Mock external dependencies (HTTP, database)
• Use tmp_path fixture for filesystem tests
• Profile with pytest --durations=10

Error: Tests are flaky

• Look for shared state between tests
• Check for test order dependencies
• Mock time-dependent code
• Avoid sleep() in tests

Error: Frontend tests crash simulator

• Always use run-tests-individually.sh, never direct xcodebuild
• Try --individual flag if all-at-once mode crashes