TDD Red Phase

TRAP 8 Defense: Tests before implementation

The Rule

Write a failing test that describes the desired behavior BEFORE writing any implementation code.

RED Phase Requirements

1. Test MUST fail - If it passes immediately, you're testing the wrong thing
2. Test MUST be specific - Testing exact expected behavior
3. Test MUST be minimal - Only test one thing
4. Test MUST compile - TypeScript clean

Test Template

describe('FeatureName', () => {
  it('should [expected behavior] when [condition]', () => {
    // Arrange - Set up test data
    const input = createTestInput();
    
    // Act - Execute the behavior
    const result = featureUnderTest(input);
    
    // Assert - Verify expected outcome
    expect(result).toBe(expectedValue);
  });
});

Before Writing Test

Ask yourself:

1. What is the smallest behavior I can test?
2. What exact input/output do I expect?
3. Am I testing behavior, not implementation?
4. Will this test fail for the right reason?

After Test Written

1. Run the test with project test command
2. Confirm it FAILS
3. Read the failure message - it should describe missing behavior
4. Proceed to GREEN phase ONLY after red confirmed

Verification

# Run test - expect FAIL
pnpm test:fast -- --run <test-file>

RED Phase Complete When

• Test is written and compiles
• Test fails when run
• Failure message describes the missing behavior
• No implementation code written yet

Failure Mode

If you skip RED:

⛔ TDD VIOLATION

Attempted: Write implementation without failing test

ACTION: Stop. Write failing test first.

Next Phase

After RED confirmed → Proceed to GREEN phase (minimal implementation to pass test)