tdd

---

name: tdd description: Test-Driven Development workflow. Write failing test first, then implement to make it pass. Use for new features, bug fixes, or refactoring with confidence. short_desc: TDD workflow: failing test first, then implement keywords: [TDD, "test-driven", "red-green-refactor", "failing test first", "write the test first", "regression test", "test-first", "tdd workflow", "failing tests", "before implementing"] argument-hint: "[feature-or-bug-description]" model: sonnet

/tdd [feature or function description]

Strict Red → Green → Refactor TDD cycle.

Usage

/tdd validate_user_email function      # TDD a specific function
/tdd rate limiting middleware          # TDD a new middleware
/tdd                                   # TDD current task from CONTEXT_STATE.md

The Cycle

🔴 RED — Write a Failing Test

1. Read the specification (task description, docstring, or requirements)

2. Identify the smallest testable behavior

3. Write ONE test that captures that behavior:

   • Test name describes behavior: test_<function>_<scenario>_<expected_outcome>
   • Assert on observable outputs, not implementation details
   • Use pytest fixtures for setup

4. Run test → confirm it fails for the right reason:

   pytest tests/ -k "your_test_name" -v
   

   • "Import error" or "AttributeError" = file/function doesn't exist yet → OK
   • "AssertionError" = function exists but wrong behavior → OK
   • Test passes without any implementation → test is wrong, rewrite it

🟢 GREEN — Make It Pass

5. Write the minimum code to make the test pass

   • No extra features, no future-proofing
   • Ugly code is fine at this stage
   • Don't optimize yet

6. Run test → confirm it passes:

   pytest tests/ -k "your_test_name" -v
   

7. Run full suite → confirm no regressions:

   pytest tests/ -q
   

🔵 REFACTOR — Clean Up

8. Improve code quality WITHOUT changing behavior:

   • Extract variables for clarity
   • Remove duplication
   • Improve naming
   • No new functionality

9. Run tests after each refactor step:

   pytest tests/ -q
   

10. Repeat from step 2 for the next behavior

Test Design Principles

One behavior per test: Each test asserts exactly one behavior Arrange-Act-Assert:

def test_validate_email_rejects_missing_at_sign():
    # Arrange
    invalid_email = "not-an-email"
    # Act
    result = validate_email(invalid_email)
    # Assert
    assert result is False

Test behaviors, not implementation:

# ❌ Tests implementation
assert validator._regex.pattern == r"^[^@]+@[^@]+\.[^@]+$"
# ✅ Tests behavior
assert validate_email("[e-mail]") is True
assert validate_email("bad-email") is False

Edge cases to always test:

• Empty input / None
• Boundary values (min/max)
• Invalid types (if not type-checked)
• Already-done state (idempotency)

KG Search Before Writing

Before writing tests, check for existing patterns:

search_code_graph("test patterns for <component type>")
hybrid_search("testing <domain> in Python")

Output Format

After completing the TDD cycle:

## TDD Summary

**Feature**: <what was implemented>
**Tests added**: N
  - test_<name>: <what it covers>
  - test_<name>: <what it covers>
**All tests**: ✅ N passing

**Refactors applied**: <what was cleaned up, or "none needed">