desenyon/tdd-guide

TDD Guide

Test-driven development skill for generating tests, analyzing coverage, and guiding red-green-refactor workflows across Jest, Pytest, JUnit, and Vitest.

---

Workflows

Generate Tests from Code

1. Provide source code (TypeScript, JavaScript, Python, Java)
2. Specify target framework (Jest, Pytest, JUnit, Vitest)
3. Run test_generator.py with requirements
4. Review generated test stubs
5. Validation: Tests compile and cover happy path, error cases, edge cases

Analyze Coverage Gaps

1. Generate coverage report from test runner (npm test -- --coverage)
2. Run coverage_analyzer.py on LCOV/JSON/XML report
3. Review prioritized gaps (P0/P1/P2)
4. Generate missing tests for uncovered paths
5. Validation: Coverage meets target threshold (typically 80%+)

TDD New Feature

1. Write failing test first (RED)
2. Run tdd_workflow.py --phase red to validate
3. Implement minimal code to pass (GREEN)
4. Run tdd_workflow.py --phase green to validate
5. Refactor while keeping tests green (REFACTOR)
6. Validation: All tests pass after each cycle

---

Examples

Test Generation — Input → Output (Pytest)

Input source function (math_utils.py):

def divide(a: float, b: float) -> float:
    if b == 0:
        raise ValueError("Cannot divide by zero")
    return a / b

Command:

python scripts/test_generator.py --input math_utils.py --framework pytest

Generated test output (test_math_utils.py):

import pytest
from math_utils import divide

class TestDivide:
    def test_divide_positive_numbers(self):
        assert divide(10, 2) == 5.0

    def test_divide_negative_numerator(self):
        assert divide(-10, 2) == -5.0

    def test_divide_float_result(self):
        assert divide(1, 3) == pytest.approx(0.333, rel=1e-3)

    def test_divide_by_zero_raises_value_error(self):
        with pytest.raises(ValueError, match="Cannot divide by zero"):
            divide(10, 0)

    def test_divide_zero_numerator(self):
        assert divide(0, 5) == 0.0

---

Coverage Analysis — Sample P0/P1/P2 Output

Command:

python scripts/coverage_analyzer.py --report lcov.info --threshold 80

Sample output:

Coverage Report — Overall: 63% (threshold: 80%)

P0 — Critical gaps (uncovered error paths):
  auth/login.py:42-58   handle_expired_token()       0% covered
  payments/process.py:91-110  handle_payment_failure()   0% covered

P1 — High-value gaps (core logic branches):
  users/service.py:77   update_profile() — else branch  0% covered
  orders/cart.py:134    apply_discount() — zero-qty guard  0% covered

P2 — Low-risk gaps (utility / helper functions):
  utils/formatting.py:12  format_currency()            0% covered

Recommended: Generate tests for P0 items first to reach 80% threshold.

---

Key Tools

| Tool | Purpose | Usage | |------|---------|-------| | test_generator.py | Generate test cases from code/requirements | python scripts/test_generator.py --input source.py --framework pytest | | coverage_analyzer.py | Parse and analyze coverage reports | python scripts/coverage_analyzer.py --report lcov.info --threshold 80 | | tdd_workflow.py | Guide red-green-refactor cycles | python scripts/tdd_workflow.py --phase red --test test_auth.py | | fixture_generator.py | Generate test data and mocks | python scripts/fixture_generator.py --entity User --count 5 |

Additional scripts: framework_adapter.py (convert between frameworks), metrics_calculator.py (quality metrics), format_detector.py (detect language/framework), output_formatter.py (CLI/desktop/CI output).

---

Input Requirements

For Test Generation:

• Source code (file path or pasted content)
• Target framework (Jest, Pytest, JUnit, Vitest)
• Coverage scope (unit, integration, edge cases)

For Coverage Analysis:

• Coverage report file (LCOV, JSON, or XML format)
• Optional: Source code for context
• Optional: Target threshold percentage

For TDD Workflow:

• Feature requirements or user story
• Current phase (RED, GREEN, REFACTOR)
• Test code and implementation status

---

Limitations

| Scope | Details | |-------|---------| | Unit test focus | Integration and E2E tests require different patterns | | Static analysis | Cannot execute tests or measure runtime behavior | | Language support | Best for TypeScript, JavaScript, Python, Java | | Report formats | LCOV, JSON, XML only; other formats need conversion | | Generated tests | Provide scaffolding; require human review for complex logic |

When to use other tools:

• E2E testing: Playwright, Cypress, Selenium
• Performance testing: k6, JMeter, Locust
• Security testing: OWASP ZAP, Burp Suite