Go Testing

This skill provides comprehensive Go testing patterns extending common testing principles with Go-specific idioms.

Testing Framework

Use the standard go test with table-driven tests as the primary pattern.

Table-Driven Tests

The idiomatic Go testing pattern:

func TestValidateEmail(t *testing.T) {
    tests := []struct {
        name    string
        email   string
        wantErr bool
    }{
        {
            name:    "valid email",
            email:   "[email protected]",
            wantErr: false,
        },
        {
            name:    "missing @",
            email:   "userexample.com",
            wantErr: true,
        },
        {
            name:    "empty string",
            email:   "",
            wantErr: 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) error = %v, wantErr %v",
                    tt.email, err, tt.wantErr)
            }
        })
    }
}

Benefits:

• Easy to add new test cases
• Clear test case documentation
• Parallel test execution with t.Parallel()
• Isolated subtests with t.Run()

Test Helpers

Use t.Helper() to mark helper functions:

func assertNoError(t *testing.T, err error) {
    t.Helper()
    if err != nil {
        t.Fatalf("unexpected error: %v", err)
    }
}

func assertEqual(t *testing.T, got, want interface{}) {
    t.Helper()
    if !reflect.DeepEqual(got, want) {
        t.Errorf("got %v, want %v", got, want)
    }
}

Benefits:

• Correct line numbers in test failures
• Reusable test utilities
• Cleaner test code

Test Fixtures

Use t.Cleanup() for resource cleanup:

func testDB(t *testing.T) *sql.DB {
    t.Helper()

    db, err := sql.Open("sqlite3", ":memory:")
    if err != nil {
        t.Fatalf("failed to open test db: %v", err)
    }

    // Cleanup runs after test completes
    t.Cleanup(func() {
        if err := db.Close(); err != nil {
            t.Errorf("failed to close db: %v", err)
        }
    })

    return db
}

func TestUserRepository(t *testing.T) {
    db := testDB(t)
    repo := NewUserRepository(db)
    // ... test logic
}

Race Detection

Always run tests with the -race flag to detect data races:

go test -race ./...

In CI/CD:

- name: Test with race detector
  run: go test -race -timeout 5m ./...

Why:

• Detects concurrent access bugs
• Prevents production race conditions
• Minimal performance overhead in tests

Coverage Analysis

Basic Coverage

go test -cover ./...

Detailed Coverage Report

go test -coverprofile=coverage.out ./...
go tool cover -html=coverage.out

Coverage Thresholds

# Fail if coverage below 80%
go test -cover ./... | grep -E 'coverage: [0-7][0-9]\.[0-9]%' && exit 1

Benchmarking

func BenchmarkValidateEmail(b *testing.B) {
    email := "[email protected]"

    b.ResetTimer()
    for i := 0; i < b.N; i++ {
        ValidateEmail(email)
    }
}

Run benchmarks:

go test -bench=. -benchmem

Compare benchmarks:

go test -bench=. -benchmem > old.txt
# make changes
go test -bench=. -benchmem > new.txt
benchstat old.txt new.txt

Mocking

Interface-Based Mocking

type UserRepository interface {
    GetUser(id string) (*User, error)
}

type mockUserRepository struct {
    users map[string]*User
    err   error
}

func (m *mockUserRepository) GetUser(id string) (*User, error) {
    if m.err != nil {
        return nil, m.err
    }
    return m.users[id], nil
}

func TestUserService(t *testing.T) {
    mock := &mockUserRepository{
        users: map[string]*User{
            "1": {ID: "1", Name: "Alice"},
        },
    }

    service := NewUserService(mock)
    // ... test logic
}

Integration Tests

Build Tags

//go:build integration
// +build integration

package user_test

func TestUserRepository_Integration(t *testing.T) {
    // ... integration test
}

Run integration tests:

go test -tags=integration ./...

Test Containers

func TestWithPostgres(t *testing.T) {
    if testing.Short() {
        t.Skip("skipping integration test")
    }

    // Setup test container
    ctx := context.Background()
    container, err := testcontainers.GenericContainer(ctx, ...)
    assertNoError(t, err)

    t.Cleanup(func() {
        container.Terminate(ctx)
    })

    // ... test logic
}

Test Organization

File Structure

package/
├── user.go
├── user_test.go          # Unit tests
├── user_integration_test.go  # Integration tests
└── testdata/             # Test fixtures
    └── users.json

Package Naming

// Black-box testing (external perspective)
package user_test

// White-box testing (internal access)
package user

Common Patterns

Testing HTTP Handlers

func TestUserHandler(t *testing.T) {
    req := httptest.NewRequest("GET", "/users/1", nil)
    rec := httptest.NewRecorder()

    handler := NewUserHandler(mockRepo)
    handler.ServeHTTP(rec, req)

    assertEqual(t, rec.Code, http.StatusOK)
}

Testing with Context

func TestWithTimeout(t *testing.T) {
    ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
    defer cancel()

    err := SlowOperation(ctx)
    if !errors.Is(err, context.DeadlineExceeded) {
        t.Errorf("expected timeout error, got %v", err)
    }
}

Best Practices

1. Use `t.Parallel()` for independent tests
2. Use `testing.Short()` to skip slow tests
3. Use `t.TempDir()` for temporary directories
4. Use `t.Setenv()` for environment variables
5. Avoid `init()` in test files
6. Keep tests focused - one behavior per test
7. Use meaningful test names - describe what's being tested

When to Use This Skill

• Writing new Go tests
• Improving test coverage
• Setting up test infrastructure
• Debugging flaky tests
• Optimizing test performance
• Implementing integration tests