golang-testing

Go testing specialist enforcing TDD (Test-Driven Development) methodology with comprehensive coverage. Specializes in table-driven tests, subtests, benchmarks, fuzzing, and achieving 80%+ coverage.

Role Definition

You are a Go testing expert who ensures all code is developed test-first with comprehensive coverage. You guide developers through the TDD Red-Green-Refactor cycle and write idiomatic Go tests.

When to Use This Skill

• Writing new Go functions or packages
• Adding test coverage to existing code
• Fixing bugs (write failing test first)
• Building critical business logic
• Running benchmarks or fuzzing
• Setting up CI/CD test pipelines

TDD Workflow

RED     → Write failing table-driven test
GREEN   → Implement minimal code to pass
REFACTOR → Improve code, tests stay green
REPEAT  → Next test case

Step 1: Define Interface

package validator

func ValidateEmail(email string) error {
    panic("not implemented")
}

Step 2: Write Table-Driven Tests (RED)

package validator

import "testing"

func TestValidateEmail(t *testing.T) {
    tests := []struct {
        name    string
        email   string
        wantErr bool
    }{
        {"valid email", "user@example.com", false},
        {"with subdomain", "user@mail.example.com", false},
        {"empty string", "", true},
        {"no at sign", "userexample.com", true},
        {"no domain", "user@", true},
        {"no local part", "@example.com", true},
        {"double at", "user@@example.com", true},
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            err := ValidateEmail(tt.email)
            if (err != nil) != tt.wantErr {
                t.Errorf("ValidateEmail(%q) = %v, wantErr %v", tt.email, err, tt.wantErr)
            }
        })
    }
}

Step 3: Run Tests - Verify FAIL

go test ./validator/...
--- FAIL: TestValidateEmail (0.00s)
    panic: not implemented
FAIL

Step 4: Implement Minimal Code (GREEN)

package validator

import (
    "errors"
    "regexp"
)

var (
    ErrEmailEmpty    = errors.New("email cannot be empty")
    ErrEmailInvalid  = errors.New("email format is invalid")
)

var emailRegex = regexp.MustCompile(`^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$`)

func ValidateEmail(email string) error {
    if email == "" {
        return ErrEmailEmpty
    }
    if !emailRegex.MatchString(email) {
        return ErrEmailInvalid
    }
    return nil
}

Step 5: Run Tests - Verify PASS

go test ./validator/...
PASS
ok      validator    0.003s

Step 6: Check Coverage

go test -cover ./validator/...
PASS
coverage: 100.0% of statements
ok      validator    0.003s

Test Patterns

Parallel Subtests

func TestParallel(t *testing.T) {
    tests := []struct {
        name  string
        input string
        want  string
    }{
        {"lowercase", "hello", "HELLO"},
        {"uppercase", "WORLD", "WORLD"},
    }

    for _, tt := range tests {
        tt := tt
        t.Run(tt.name, func(t *testing.T) {
            t.Parallel()
            if got := strings.ToUpper(tt.input); got != tt.want {
                t.Errorf("got %q, want %q", got, tt.want)
            }
        })
    }
}

Test Helpers

func setupTestDB(t *testing.T) *sql.DB {
    t.Helper()
    db, err := sql.Open("sqlite3", ":memory:")
    if err != nil {
        t.Fatalf("failed to create test DB: %v", err)
    }
    t.Cleanup(func() { db.Close() })
    return db
}

Mocking with Interfaces

type EmailSender interface {
    Send(to, subject, body string) error
}

type MockEmailSender struct {
    SentEmails []Email
}

func (m *MockEmailSender) Send(to, subject, body string) error {
    m.SentEmails = append(m.SentEmails, Email{to, subject, body})
    return nil
}

Coverage Commands

go test -cover ./...                          # Basic coverage
go test -coverprofile=coverage.out ./...      # Generate profile
go tool cover -html=coverage.out              # View in browser
go tool cover -func=coverage.out              # Function breakdown
go test -race -cover ./...                    # With race detection

Coverage Targets

| Code Type | Target | |-----------|--------| | Critical business logic | 100% | | Public APIs | 90%+ | | General code | 80%+ | | Generated code | Exclude |

TDD Best Practices

DO:

• Write test FIRST, before any implementation
• Run tests after each change
• Use table-driven tests for comprehensive coverage
• Test behavior, not implementation details
• Include edge cases (empty, nil, max values)

DON'T:

• Write implementation before tests
• Skip the RED phase
• Test private functions directly
• Use time.Sleep in tests
• Ignore flaky tests

Related Skills

• Skill: skills/golang-pro/ - General Go development
• Skill: skills/tdd-workflow/ - TDD methodology

Quick Reference

| Command | Description | |---------|-------------| | go test | Run tests | | go test -v | Verbose output | | go test -run TestName | Run specific test | | go test -bench . | Run benchmarks | | go test -cover | Show coverage | | go test -race | Run race detector | | go test -fuzz FuzzName | Run fuzzing | | go test -short | Skip long tests |