test-driven-development

Original：🇺🇸 English
Translated

Use when writing new functions, adding features, fixing bugs, or refactoring by applying TDD principles - write failing tests before implementation code, make them pass, then refactor.

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NPX Install

npx skill4agent add thebushidocollective/han test-driven-development

Tags

Translated version includes tags in frontmatter
test-driven-developmenttdd-workflowcode-refactoringbackend-testingfrontend-testing

SKILL.md Content

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Test-Driven Development (TDD)

Red → Green → Refactor cycle for all code changes.

The TDD Cycle

  1. RED: Write failing test
  2. GREEN: Write minimal code to pass
  3. REFACTOR: Improve code quality

Repeat for each requirement

When to Apply TDD

✅ Always use TDD for:
  • New functions/methods
  • New features
  • Bug fixes (reproduce first)
  • Refactoring existing code
  • API changes
❌ Skip TDD for:
  • UI styling tweaks
  • Configuration changes
  • Documentation updates

Process

1. Write Failing Test First

elixir
# Start with test
test "calculates total with tax" do
  result = Calculator.calculate_total([100, 200])
  assert Money.equal?(result, Money.new(:USD, 324))
end

# Run test - should FAIL
mix test

2. Implement Minimal Code

elixir
# Just enough to pass
def calculate_total(prices) do
  prices |> Enum.sum() |> Kernel.*(1.08) |> Money.new(:USD)
end

3. Refactor

Extract constants, improve naming, etc.

Test Patterns by Stack

Backend (Elixir)

  • File: 
    test/path/module_test.exs
  • Pattern: 
    apps/api/test/your_app/task/task_test.exs

Frontend (TypeScript)

  • File: 
    ComponentName.test.tsx
  • Pattern: 
    mobile/libraries/atorasu/atoms/Button/Button.test.tsx

Critical Rules

  • Tests MUST fail first (verify test works)
  • One test per requirement
  • Test behavior, not implementation
  • Run FULL test suite before commit
  • NEVER skip failing tests

Common Pitfalls

  • Writing implementation before test
  • Tests that pass without implementation (false positive)
  • Testing implementation details instead of behavior
  • Not running test to verify it fails first

Verification

bash
# Backend
mix test path/to/test.exs

# Frontend
yarn test path/to/test.tsx