tdd-red

Write comprehensive failing tests following TDD red phase principles.

[Extended thinking: Generates failing tests that properly define expected behavior using test-automator agent.]

Role

Generate failing tests using Task tool with subagent_type="unit-testing::test-automator".

Prompt Template

"Generate comprehensive FAILING tests for: (use the user's prompt)

Core Requirements

1. Test Structure

   • Framework-appropriate setup (Jest/pytest/JUnit/Go/RSpec)
   • Arrange-Act-Assert pattern
   • should_X_when_Y naming convention
   • Isolated fixtures with no interdependencies

2. Behavior Coverage

   • Happy path scenarios
   • Edge cases (empty, null, boundary values)
   • Error handling and exceptions
   • Concurrent access (if applicable)

3. Failure Verification

   • Tests MUST fail when run
   • Failures for RIGHT reasons (not syntax/import errors)
   • Meaningful diagnostic error messages
   • No cascading failures

4. Test Categories

   • Unit: Isolated component behavior
   • Integration: Component interaction
   • Contract: API/interface contracts
   • Property: Mathematical invariants

Framework Patterns

JavaScript/TypeScript (Jest/Vitest)

• Mock dependencies with vi.fn() or jest.fn()
• Use @testing-library for React components
• Property tests with fast-check

Python (pytest)

• Fixtures with appropriate scopes
• Parametrize for multiple test cases
• Hypothesis for property-based tests

Go

• Table-driven tests with subtests
• t.Parallel() for parallel execution
• Use testify/assert for cleaner assertions

Ruby (RSpec)

• let for lazy loading, let! for eager
• Contexts for different scenarios
• Shared examples for common behavior

Quality Checklist

• Readable test names documenting intent
• One behavior per test
• No implementation leakage
• Meaningful test data (not 'foo'/'bar')
• Tests serve as living documentation

Anti-Patterns to Avoid

• Tests passing immediately
• Testing implementation vs behavior
• Complex setup code
• Multiple responsibilities per test
• Brittle tests tied to specifics

Edge Case Categories

• Null/Empty: undefined, null, empty string/array/object
• Boundaries: min/max values, single element, capacity limits
• Special Cases: Unicode, whitespace, special characters
• State: Invalid transitions, concurrent modifications
• Errors: Network failures, timeouts, permissions

Output Requirements

• Complete test files with imports
• Documentation of test purpose
• Commands to run and verify failures
• Metrics: test count, coverage areas
• Next steps for green phase"

Validation

After generation:

1. Run tests - confirm they fail
2. Verify helpful failure messages
3. Check test independence
4. Ensure comprehensive coverage

Example (Minimal)

// auth.service.test.ts
describe("AuthService", () => {
  let authService: AuthService;
  let mockUserRepo: jest.Mocked<UserRepository>;

  beforeEach(() => {
    mockUserRepo = { findByEmail: jest.fn() } as any;
    authService = new AuthService(mockUserRepo);
  });

  it("should_return_token_when_valid_credentials", async () => {
    const user = { id: "1", email: "test@example.com", passwordHash: "hashed" };
    mockUserRepo.findByEmail.mockResolvedValue(user);

    const result = await authService.authenticate("test@example.com", "pass");

    expect(result.success).toBe(true);
    expect(result.token).toBeDefined();
  });

  it("should_fail_when_user_not_found", async () => {
    mockUserRepo.findByEmail.mockResolvedValue(null);

    const result = await authService.authenticate("none@example.com", "pass");

    expect(result.success).toBe(false);
    expect(result.error).toBe("INVALID_CREDENTIALS");
  });
});

Test requirements: (use the user's prompt)

Output Format

<result>
  <analysis>Brief analysis</analysis>
  <solution>Implementation</solution>
  <considerations>Trade-offs and notes</considerations>
</result>