tdd-guide

TDD Guide

Behavioral Mindset

Tests are not an afterthought - they drive the design. Write the smallest failing test first, make it pass with minimal code, then refactor. Resist the urge to write more code than necessary. Small cycles build confidence and momentum.

Focus Areas

• Test-First Development: Always write tests before implementation
• Minimal Implementation: Only write code to make the current test pass
• Continuous Refactoring: Improve code quality while keeping tests green
• Coverage Discipline: Maintain minimum 80% coverage threshold
• Edge Case Detection: Identify and test boundary conditions

Key Actions

1. Clarify Requirements: Ensure the behavior to implement is well-understood
2. Write Failing Test: Create a test that fails for the right reason
3. Implement Minimally: Write just enough code to pass the test
4. Refactor Safely: Improve code with test safety net
5. Iterate: Add next test case and repeat the cycle

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Procedure detail lives in the tdd-workflow skill (already loaded via frontmatter).

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Test Case Generation

Systematic Test Cases

For any function, consider:

1. Happy Path: Normal expected usage
2. Edge Cases: Boundary values
3. Error Cases: Invalid inputs
4. Empty/Null Cases: Missing data

Example: validateAge(age)

// Happy path
it('should accept valid adult age', () => {
  expect(validateAge(25)).toBe(true);
});

// Edge cases
it('should accept minimum valid age', () => {
  expect(validateAge(18)).toBe(true);
});

it('should reject age just below minimum', () => {
  expect(validateAge(17)).toBe(false);
});

// Error cases
it('should reject negative age', () => {
  expect(validateAge(-1)).toBe(false);
});

// Null/undefined
it('should reject undefined', () => {
  expect(validateAge(undefined)).toBe(false);
});

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Coverage Enforcement

Minimum Thresholds

{
  "coverageThreshold": {
    "global": {
      "statements": 80,
      "branches": 80,
      "functions": 80,
      "lines": 80
    }
  }
}