Go Testing Patterns
Comprehensive Go testing patterns for writing reliable, maintainable tests following TDD methodology.
When to Activate
- Writing new Go functions or methods
- Adding test coverage to existing code
- Creating benchmarks for performance-critical code
- Implementing fuzz tests for input validation
- Following TDD workflow in Go projects
TDD Workflow for Go
The RED-GREEN-REFACTOR Cycle
RED → Write a failing test first
GREEN → Write minimal code to pass the test
REFACTOR → Improve code while keeping tests green
REPEAT → Continue with next requirementStep-by-Step TDD in Go
// Step 1: Define the interface/signature
// calculator.go
package calculator
func Add(a, b int) int {
panic("not implemented") // Placeholder
}
// Step 2: Write failing test (RED)
// calculator_test.go
package calculator
import "testing"
func TestAdd(t *testing.T) {
got := Add(2, 3)
want := 5
if got != want {
t.Errorf("Add(2, 3) = %d; want %d", got, want)
}
}
// Step 3: Run test - verify FAIL
// $ go test
// --- FAIL: TestAdd (0.00s)
// panic: not implemented
// Step 4: Implement minimal code (GREEN)
func Add(a, b int) int {
return a + b
}
// Step 5: Run test - verify PASS
// $ go test
// PASS
// Step 6: Refactor if needed, verify tests still passTable-Driven Tests
The standard pattern for Go tests. Enables comprehensive coverage with minimal code.
func TestAdd(t *testing.T) {
tests := []struct {
name string
a, b int
expected int
}{
{"positive numbers", 2, 3, 5},
{"negative numbers", -1, -2, -3},
{"zero values", 0, 0, 0},
{"mixed signs", -1, 1, 0},
{"large numbers", 1000000, 2000000, 3000000},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
got := Add(tt.a, tt.b)
if got != tt.expected {
t.Errorf("Add(%d, %d) = %d; want %d",
tt.a, tt.b, got, tt.expected)
}
})
}
}Table-Driven Tests with Error Cases
func TestParseConfig(t *testing.T) {
tests := []struct {
name string
input string
want *Config
wantErr bool
}{
{
name: "valid config",
input: `{"host": "localhost", "port": 8080}`,
want: &Config{Host: "localhost", Port: 8080},
},
{
name: "invalid JSON",
input: `{invalid}`,
wantErr: true,
},
{
name: "empty input",
input: "",
wantErr: true,
},
{
name: "minimal config",
input: `{}`,
want: &Config{}, // Zero value config
},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
got, err := ParseConfig(tt.input)
if tt.wantErr {
if err == nil {
t.Error("expected error, got nil")
}
return
}
if err != nil {
t.Fatalf("unexpected error: %v", err)
}
if !reflect.DeepEqual(got, tt.want) {
t.Errorf("got %+v; want %+v", got, tt.want)
}
})
}
}Subtests and Sub-benchmarks
Organizing Related Tests
func TestUser(t *testing.T) {
// Setup shared by all subtests
db := setupTestDB(t)
t.Run("Create", func(t *testing.T) {
user := &User{Name: "Alice"}
err := db.CreateUser(user)
if err != nil {
t.Fatalf("CreateUser failed: %v", err)
}
if user.ID == "" {
t.Error("expected user ID to be set")
}
})
t.Run("Get", func(t *testing.T) {
user, err := db.GetUser("alice-id")
if err != nil {
t.Fatalf("GetUser failed: %v", err)
}
if user.Name != "Alice" {
t.Errorf("got name %q; want %q", user.Name, "Alice")
}
})
t.Run("Update", func(t *testing.T) {
// ...
})
t.Run("Delete", func(t *testing.T) {
// ...
})
}Parallel Subtests
func TestParallel(t *testing.T) {
tests := []struct {
name string
input string
}{
{"case1", "input1"},
{"case2", "input2"},
{"case3", "input3"},
}
for _, tt := range tests {
tt := tt // Capture range variable
t.Run(tt.name, func(t *testing.T) {
t.Parallel() // Run subtests in parallel
result := Process(tt.input)
// assertions...
_ = result
})
}
}Test Helpers
Helper Functions
func setupTestDB(t *testing.T) *sql.DB {
t.Helper() // Marks this as a helper function
db, err := sql.Open("sqlite3", ":memory:")
if err != nil {
t.Fatalf("failed to open database: %v", err)
}
// Cleanup when test finishes
t.Cleanup(func() {
db.Close()
})
// Run migrations
if _, err := db.Exec(schema); err != nil {
t.Fatalf("failed to create schema: %v", err)
}
return db
}
func assertNoError(t *testing.T, err error) {
t.Helper()
if err != nil {
t.Fatalf("unexpected error: %v", err)
}
}
func assertEqual[T comparable](t *testing.T, got, want T) {
t.Helper()
if got != want {
t.Errorf("got %v; want %v", got, want)
}
}Temporary Files and Directories
func TestFileProcessing(t *testing.T) {
// Create temp directory - automatically cleaned up
tmpDir := t.TempDir()
// Create test file
testFile := filepath.Join(tmpDir, "test.txt")
err := os.WriteFile(testFile, []byte("test content"), 0644)
if err != nil {
t.Fatalf("failed to create test file: %v", err)
}
// Run test
result, err := ProcessFile(testFile)
if err != nil {
t.Fatalf("ProcessFile failed: %v", err)
}
// Assert...
_ = result
}Golden Files
Testing against expected output files stored in testdata/.
var update = flag.Bool("update", false, "update golden files")
func TestRender(t *testing.T) {
tests := []struct {
name string
input Template
}{
{"simple", Template{Name: "test"}},
{"complex", Template{Name: "test", Items: []string{"a", "b"}}},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
got := Render(tt.input)
golden := filepath.Join("testdata", tt.name+".golden")
if *update {
// Update golden file: go test -update
err := os.WriteFile(golden, got, 0644)
if err != nil {
t.Fatalf("failed to update golden file: %v", err)
}
}
want, err := os.ReadFile(golden)
if err != nil {
t.Fatalf("failed to read golden file: %v", err)
}
if !bytes.Equal(got, want) {
t.Errorf("output mismatch:\ngot:\n%s\nwant:\n%s", got, want)
}
})
}
}Mocking with Interfaces
Interface-Based Mocking
// Define interface for dependencies
type UserRepository interface {
GetUser(id string) (*User, error)
SaveUser(user *User) error
}
// Production implementation
type PostgresUserRepository struct {
db *sql.DB
}
func (r *PostgresUserRepository) GetUser(id string) (*User, error) {
// Real database query
}
// Mock implementation for tests
type MockUserRepository struct {
GetUserFunc func(id string) (*User, error)
SaveUserFunc func(user *User) error
}
func (m *MockUserRepository) GetUser(id string) (*User, error) {
return m.GetUserFunc(id)
}
func (m *MockUserRepository) SaveUser(user *User) error {
return m.SaveUserFunc(user)
}
// Test using mock
func TestUser