TDD RED Phase

Version: v0.17.1

Guide through RED phase: writing failing tests and verifying expected failures.

When to Use

• Starting new feature implementation
• User issues "First-Step" (IDPF-Structured)
• User issues "Start-Story [ID]" (IDPF-Agile)
• Beginning new TDD iteration

Objective

Write a test that fails for the right reason.

Correct failure: Feature doesn't exist, behavior not implemented, failure message clear Incorrect failure: Syntax error, missing imports, test passes unexpectedly

Workflow

Step 1: Identify Testable Behavior One test per behavior, one behavior per test.

Good: "GET /users returns 200 status"
Bad: "User management works" (too broad)

Step 2: Write Failing Test (Single Code Block)

TASK: [Description]
STEP 1: Create/open test file
STEP 2: Add imports
STEP 3: Write complete test (AAA: Arrange-Act-Assert)
STEP 4: Save file
STEP 5: Run test command
STEP 6: Verify test FAILS with expected message
STEP 7: Report: Did test fail as expected?

Step 3: Execute and Verify

• Test executed without syntax errors
• Test failed (not passed)
• Failure message indicates missing implementation

Step 4: Analyze

• Fails as expected → "Done-Next-Step" → GREEN phase
• Passes unexpectedly → Revise test
• Errors instead of fails → Fix test code

Best Practices

• Write minimal tests (single assertion)
• Clear test names: test_[feature]_[scenario]_[expected_result]
• Descriptive assertions with helpful failure messages

Anti-Patterns

• Writing implementation first
• Skipping failure verification
• Tolerating test errors

Checklist

• Test complete and syntactically correct
• Test FAILS (not passes, not errors)
• Failure message clearly indicates missing implementation
• User reported via "Done-Next-Step"

End of TDD RED Phase Skill