Test-Driven Development (TDD) Best Practices

This skill guides rigorous test-first development following the Red-Green-Refactor cycle.

When to Use

Activate when:

• •Implementing new features
• •Fixing bugs
• •Refactoring existing code
• •Making any code changes

TDD Core Principles

Red-Green-Refactor Cycle

1. •Red - Write tests FIRST before implementation
2. •Green - Write minimal code to pass tests
3. •Refactor - Clean up while keeping tests green

Test Quality Standards

Write Tests First:

• •Tests should be minimal and focused on single behaviors
• •Tests are documentation - they clearly show expected behavior
• •If you can't easily test it, the design is wrong - refactor for testability

Test Organization:

• •Use table-driven tests for multiple inputs/scenarios in Go
• •Test file naming: *_test.go for unit tests, e2e_test.go for integration
• •Always test error cases and edge conditions

Test Types:

• •Unit tests - Mock external dependencies (network, filesystem, time)
• •Integration tests - Validate real component interactions
• •End-to-end tests - Cover critical user workflows

Assertion Libraries

Go Testing:

• •Use testify/require for assertions that should stop test execution
• •Use testify/assert for assertions that should continue test execution

Design for Testability

✅ Testable patterns:

• •Dependency injection
• •Interface-based abstractions
• •Pure functions
• •Isolated side effects

❌ Hard to test (redesign):

• •Global state
• •Hidden dependencies
• •Tight coupling
• •Side effects mixed with logic

TDD Workflow

1. •Write failing test(s) embodying acceptance criteria
2. •Run tests - verify they fail for the right reason
3. •Implement minimal code to make tests pass
4. •Run tests - verify they all pass
5. •Refactor for quality while keeping tests green
6. •Repeat

Quality Gates

Before considering work "done":

• • All tests pass locally and in CI
• • Coverage ≥ 90% lines/branches
• • Error cases are tested
• • Edge conditions are tested
• • Tests document expected behavior clearly