How to Write Unit Tests in Go Using go test and the Testing Package
Unit testing in Go is one of those things that seems intimidating at first but becomes second nature once you get the hang of it. Go’s built-in testing framework is refreshingly simple compared to other languages – no external dependencies, no complex setup, just write your tests and run go test. This guide will walk you through everything from basic test structure to advanced testing patterns, real-world examples, and the gotchas that’ll save you hours of debugging down the road.
How Go’s Testing Framework Works
Go’s testing approach is beautifully minimalist. The testing package provides everything you need right out of the box. Tests live alongside your source code in files ending with _test.go, and any function starting with Test that takes a *testing.T parameter becomes a test case.
When you run go test, the Go toolchain automatically discovers these test files, compiles them into a temporary binary, and executes each test function. The testing runtime handles parallel execution, timeout management, and result reporting. It’s fast, efficient, and designed to encourage testing as a first-class citizen in your development workflow.
Here’s the basic anatomy of a Go test:
package calculator
import "testing"
func TestAdd(t *testing.T) {
result := Add(2, 3)
expected := 5
if result != expected {
t.Errorf("Add(2, 3) = %d; want %d", result, expected)
}
}
Step-by-Step Implementation Guide
Let’s build a complete testing setup from scratch. We’ll create a simple HTTP handler and test it thoroughly to demonstrate different testing patterns.
First, create your main code file server.go:
package main
import (
"encoding/json"
"fmt"
"net/http"
"strconv"
)
type Calculator struct{}
func (c *Calculator) Add(a, b int) int {
return a + b
}
func (c *Calculator) Divide(a, b int) (float64, error) {
if b == 0 {
return 0, fmt.Errorf("division by zero")
}
return float64(a) / float64(b), nil
}
func (c *Calculator) HandleCalculation(w http.ResponseWriter, r *http.Request) {
if r.Method != http.MethodPost {
http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
return
}
var req struct {
A int `json:"a"`
B int `json:"b"`
Op string `json:"operation"`
}
if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
http.Error(w, "Invalid JSON", http.StatusBadRequest)
return
}
var result interface{}
var err error
switch req.Op {
case "add":
result = c.Add(req.A, req.B)
case "divide":
result, err = c.Divide(req.A, req.B)
if err != nil {
http.Error(w, err.Error(), http.StatusBadRequest)
return
}
default:
http.Error(w, "Unknown operation", http.StatusBadRequest)
return
}
w.Header().Set("Content-Type", "application/json")
json.NewEncoder(w).Encode(map[string]interface{}{"result": result})
}
Now create server_test.go with comprehensive tests:
package main
import (
"bytes"
"encoding/json"
"net/http"
"net/http/httptest"
"testing"
)
func TestCalculator_Add(t *testing.T) {
calc := &Calculator{}
tests := []struct {
name string
a, b int
want int
}{
{"positive numbers", 2, 3, 5},
{"negative numbers", -1, -2, -3},
{"zero values", 0, 5, 5},
{"large numbers", 1000000, 2000000, 3000000},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
got := calc.Add(tt.a, tt.b)
if got != tt.want {
t.Errorf("Add(%d, %d) = %d, want %d", tt.a, tt.b, got, tt.want)
}
})
}
}
func TestCalculator_Divide(t *testing.T) {
calc := &Calculator{}
t.Run("valid division", func(t *testing.T) {
result, err := calc.Divide(10, 2)
if err != nil {
t.Fatalf("unexpected error: %v", err)
}
if result != 5.0 {
t.Errorf("Divide(10, 2) = %f, want 5.0", result)
}
})
t.Run("division by zero", func(t *testing.T) {
_, err := calc.Divide(10, 0)
if err == nil {
t.Fatal("expected error for division by zero")
}
if err.Error() != "division by zero" {
t.Errorf("unexpected error message: %v", err)
}
})
}
func TestCalculator_HandleCalculation(t *testing.T) {
calc := &Calculator{}
tests := []struct {
name string
method string
body interface{}
wantStatus int
wantBody string
}{
{
name: "successful addition",
method: http.MethodPost,
body: map[string]interface{}{"a": 5, "b": 3, "operation": "add"},
wantStatus: http.StatusOK,
wantBody: `{"result":8}`,
},
{
name: "successful division",
method: http.MethodPost,
body: map[string]interface{}{"a": 10, "b": 2, "operation": "divide"},
wantStatus: http.StatusOK,
wantBody: `{"result":5}`,
},
{
name: "division by zero",
method: http.MethodPost,
body: map[string]interface{}{"a": 10, "b": 0, "operation": "divide"},
wantStatus: http.StatusBadRequest,
wantBody: "division by zero\n",
},
{
name: "invalid method",
method: http.MethodGet,
body: nil,
wantStatus: http.StatusMethodNotAllowed,
wantBody: "Method not allowed\n",
},
{
name: "unknown operation",
method: http.MethodPost,
body: map[string]interface{}{"a": 5, "b": 3, "operation": "multiply"},
wantStatus: http.StatusBadRequest,
wantBody: "Unknown operation\n",
},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
var body bytes.Buffer
if tt.body != nil {
json.NewEncoder(&body).Encode(tt.body)
}
req := httptest.NewRequest(tt.method, "/calculate", &body)
req.Header.Set("Content-Type", "application/json")
recorder := httptest.NewRecorder()
calc.HandleCalculation(recorder, req)
if recorder.Code != tt.wantStatus {
t.Errorf("status = %d, want %d", recorder.Code, tt.wantStatus)
}
if recorder.Body.String() != tt.wantBody {
t.Errorf("body = %q, want %q", recorder.Body.String(), tt.wantBody)
}
})
}
}
func BenchmarkCalculator_Add(b *testing.B) {
calc := &Calculator{}
for i := 0; i < b.N; i++ {
calc.Add(123, 456)
}
}
func BenchmarkCalculator_HandleCalculation(b *testing.B) {
calc := &Calculator{}
body := bytes.NewBufferString(`{"a":5,"b":3,"operation":"add"}`)
req := httptest.NewRequest(http.MethodPost, "/calculate", body)
req.Header.Set("Content-Type", "application/json")
b.ResetTimer()
for i := 0; i < b.N; i++ {
recorder := httptest.NewRecorder()
calc.HandleCalculation(recorder, req)
body.Reset()
body.WriteString(`{"a":5,"b":3,"operation":"add"}`)
req.Body = body
}
}
Run your tests with various options:
# Run all tests
go test
# Run tests with verbose output
go test -v
# Run specific test
go test -run TestCalculator_Add
# Run tests with coverage
go test -cover
# Generate detailed coverage report
go test -coverprofile=coverage.out
go tool cover -html=coverage.out
# Run benchmarks
go test -bench=.
# Run tests in parallel with race detection
go test -race -parallel=4
Real-World Examples and Use Cases
Let's explore some practical testing scenarios you'll encounter in production systems. Here's how to test database interactions using dependency injection:
package user
import (
"database/sql"
"fmt"
)
type UserRepository interface {
GetUser(id int) (*User, error)
CreateUser(user *User) error
}
type User struct {
ID int `json:"id"`
Name string `json:"name"`
Email string `json:"email"`
}
type PostgresUserRepository struct {
db *sql.DB
}
func (r *PostgresUserRepository) GetUser(id int) (*User, error) {
user := &User{}
query := "SELECT id, name, email FROM users WHERE id = $1"
err := r.db.QueryRow(query, id).Scan(&user.ID, &user.Name, &user.Email)
if err != nil {
if err == sql.ErrNoRows {
return nil, fmt.Errorf("user not found")
}
return nil, err
}
return user, nil
}
type UserService struct {
repo UserRepository
}
func (s *UserService) GetUserProfile(id int) (*User, error) {
if id <= 0 {
return nil, fmt.Errorf("invalid user ID")
}
return s.repo.GetUser(id)
}
And the corresponding test file:
package user
import (
"fmt"
"testing"
)
// Mock implementation for testing
type MockUserRepository struct {
users map[int]*User
err error
}
func (m *MockUserRepository) GetUser(id int) (*User, error) {
if m.err != nil {
return nil, m.err
}
user, exists := m.users[id]
if !exists {
return nil, fmt.Errorf("user not found")
}
return user, nil
}
func (m *MockUserRepository) CreateUser(user *User) error {
if m.err != nil {
return m.err
}
m.users[user.ID] = user
return nil
}
func TestUserService_GetUserProfile(t *testing.T) {
mockRepo := &MockUserRepository{
users: map[int]*User{
1: {ID: 1, Name: "John Doe", Email: "john@example.com"},
2: {ID: 2, Name: "Jane Smith", Email: "jane@example.com"},
},
}
service := &UserService{repo: mockRepo}
t.Run("valid user ID", func(t *testing.T) {
user, err := service.GetUserProfile(1)
if err != nil {
t.Fatalf("unexpected error: %v", err)
}
if user.Name != "John Doe" {
t.Errorf("expected name 'John Doe', got %s", user.Name)
}
})
t.Run("invalid user ID", func(t *testing.T) {
_, err := service.GetUserProfile(-1)
if err == nil {
t.Fatal("expected error for invalid ID")
}
expected := "invalid user ID"
if err.Error() != expected {
t.Errorf("expected error %q, got %q", expected, err.Error())
}
})
t.Run("user not found", func(t *testing.T) {
_, err := service.GetUserProfile(999)
if err == nil {
t.Fatal("expected error for non-existent user")
}
if err.Error() != "user not found" {
t.Errorf("unexpected error: %v", err)
}
})
t.Run("repository error", func(t *testing.T) {
mockRepo.err = fmt.Errorf("database connection failed")
_, err := service.GetUserProfile(1)
if err == nil {
t.Fatal("expected database error")
}
if err.Error() != "database connection failed" {
t.Errorf("unexpected error: %v", err)
}
})
}
For testing concurrent code, here's a practical example:
func TestConcurrentAccess(t *testing.T) {
const numGoroutines = 100
const numOperations = 1000
counter := &SafeCounter{count: 0}
var wg sync.WaitGroup
wg.Add(numGoroutines)
for i := 0; i < numGoroutines; i++ {
go func() {
defer wg.Done()
for j := 0; j < numOperations; j++ {
counter.Increment()
}
}()
}
wg.Wait()
expected := numGoroutines * numOperations
if counter.Value() != expected {
t.Errorf("expected %d, got %d", expected, counter.Value())
}
}
Comparisons with Alternative Testing Approaches
While Go's built-in testing is powerful, it's worth understanding how it compares to external testing libraries and approaches from other languages:
| Feature | Go Built-in | Testify | Ginkgo/Gomega | JUnit (Java) |
|---|---|---|---|---|
| Setup Required | None | go get dependency | go get dependencies | Maven/Gradle setup |
| Assertion Style | Manual if/error checks | assert.Equal(t, expected, actual) | Expect(actual).To(Equal(expected)) | assertEquals(expected, actual) |
| Mocking | Manual/interfaces | Built-in mock objects | Manual/interfaces | Mockito framework |
| BDD Support | Limited | Suite support | Full BDD syntax | External libraries |
| Performance | Excellent | Good | Good | Slower startup |
Here's a comparison of the same test written with different approaches:
// Built-in testing
func TestUserAge_Builtin(t *testing.T) {
user := &User{Age: 25}
if user.IsAdult() != true {
t.Errorf("expected user to be adult")
}
}
// With Testify
func TestUserAge_Testify(t *testing.T) {
user := &User{Age: 25}
assert.True(t, user.IsAdult(), "expected user to be adult")
}
// With Ginkgo/Gomega
var _ = Describe("User", func() {
Context("when user is 25 years old", func() {
It("should be considered an adult", func() {
user := &User{Age: 25}
Expect(user.IsAdult()).To(BeTrue())
})
})
})
Best Practices and Common Pitfalls
After years of Go testing in production, here are the patterns that consistently work well and the mistakes that'll bite you:
- Use table-driven tests - They're more maintainable and catch edge cases you wouldn't think of
- Test interfaces, not implementations - This makes your tests more resilient to refactoring
- Keep tests independent - Each test should be able to run in isolation without depending on others
- Use meaningful test names -
TestUserService_GetUser_ReturnsErrorWhenUserNotFoundis better thanTestGetUser - Don't ignore the race detector - Run
go test -raceregularly, especially for concurrent code
Common pitfalls to avoid:
// BAD: Testing implementation details
func TestUserService_GetUser_Bad(t *testing.T) {
service := &UserService{}
// This test breaks when you change internal implementation
if service.cache == nil {
t.Error("cache should be initialized")
}
}
// GOOD: Testing behavior
func TestUserService_GetUser_Good(t *testing.T) {
service := &UserService{repo: &MockUserRepository{}}
user, err := service.GetUser(1)
if err != nil {
t.Fatalf("unexpected error: %v", err)
}
if user == nil {
t.Error("expected user to be returned")
}
}
// BAD: Ignoring cleanup
func TestFileOperations_Bad(t *testing.T) {
file, _ := os.Create("test.txt")
// Test code...
// File left behind!
}
// GOOD: Proper cleanup
func TestFileOperations_Good(t *testing.T) {
file, err := os.Create("test.txt")
if err != nil {
t.Fatalf("failed to create test file: %v", err)
}
defer os.Remove("test.txt")
// Test code...
}
// BAD: Overly complex setup
func TestComplexSetup_Bad(t *testing.T) {
// 50 lines of setup code
// Tests become unreadable
}
// GOOD: Use helper functions
func TestComplexSetup_Good(t *testing.T) {
server := setupTestServer(t)
client := setupTestClient(t)
// Clear test logic
}
func setupTestServer(t *testing.T) *httptest.Server {
// Setup logic here
return httptest.NewServer(handler)
}
Performance considerations for your test suite:
// Use build tags for integration tests
// +build integration
package main
import "testing"
func TestDatabaseIntegration(t *testing.T) {
// Expensive database tests here
}
// Run with: go test -tags=integration
Here's a benchmark comparison showing the performance impact of different testing approaches:
| Test Type | Execution Time | Memory Usage | Best Use Case |
|---|---|---|---|
| Unit Tests (Built-in) | ~0.5ms per test | Minimal | Business logic, algorithms |
| HTTP Tests (httptest) | ~2-5ms per test | Low | API handlers, middleware |
| Database Tests (testcontainers) | ~50-200ms per test | High | Data layer integration |
| End-to-End Tests | ~1-10s per test | Very High | Critical user journeys |
Finally, here's a complete example of a production-ready test setup with all the bells and whistles:
package api
import (
"context"
"encoding/json"
"net/http"
"net/http/httptest"
"os"
"strings"
"testing"
"time"
)
func TestMain(m *testing.M) {
// Global setup
setupTestDatabase()
// Run tests
code := m.Run()
// Global teardown
teardownTestDatabase()
os.Exit(code)
}
func TestAPIServer_Integration(t *testing.T) {
if testing.Short() {
t.Skip("skipping integration test in short mode")
}
server := setupTestServer(t)
defer server.Close()
client := &http.Client{Timeout: 5 * time.Second}
t.Run("health check", func(t *testing.T) {
resp, err := client.Get(server.URL + "/health")
if err != nil {
t.Fatalf("health check failed: %v", err)
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusOK {
t.Errorf("expected status 200, got %d", resp.StatusCode)
}
})
t.Run("user creation workflow", func(t *testing.T) {
// Create user
userData := `{"name":"Test User","email":"test@example.com"}`
resp, err := client.Post(
server.URL+"/users",
"application/json",
strings.NewReader(userData),
)
if err != nil {
t.Fatalf("user creation failed: %v", err)
}
defer resp.Body.Close()
if resp.StatusCode != http.StatusCreated {
t.Errorf("expected status 201, got %d", resp.StatusCode)
}
var user struct {
ID int `json:"id"`
Name string `json:"name"`
Email string `json:"email"`
}
if err := json.NewDecoder(resp.Body).Decode(&user); err != nil {
t.Fatalf("failed to decode response: %v", err)
}
// Verify user was created
if user.ID == 0 {
t.Error("expected user ID to be set")
}
if user.Name != "Test User" {
t.Errorf("expected name 'Test User', got %s", user.Name)
}
})
}
func setupTestServer(t *testing.T) *httptest.Server {
handler := setupRoutes()
server := httptest.NewServer(handler)
t.Cleanup(func() {
server.Close()
})
return server
}
The key to successful testing in Go is starting simple and gradually adding complexity as your needs grow. The built-in testing package handles 90% of use cases beautifully, and when you need more advanced features, the ecosystem provides excellent options. Remember that good tests are documentation for your code - they should clearly express what your code does and handle edge cases that might not be obvious from reading the implementation.
For more advanced testing patterns and the complete testing package documentation, check out the official Go testing documentation and the Go testing tutorial.
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