TDD Guide

Domain: Engineering - Core | Skill: tdd-guide | Source: engineering-team/tdd-guide/SKILL.md

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TDD Guide

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

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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

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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

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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.

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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).

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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

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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