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 firstGREEN → Write minimal code to pass the testREFACTOR → Improve code while keeping tests greenREPEAT → Continue with next requirementStep-by-Step TDD in Go
go
// Step 1: Define the interface/signature// calculator.gopackage calculator
func Add(a, b int) int { panic("not implemented") // Placeholder}
// Step 2: Write failing test (RED)// calculator_test.gopackage 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.
go
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
go
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
go
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
go
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
go
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
go
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/.
go
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
go
// Define interface for dependenciestype UserRepository interface { GetUser(id string) (*User, error) SaveUser(user *User) error}
// Production implementationtype PostgresUserRepository struct { db *sql.DB}
func (r *PostgresUserRepository) GetUser(id string) (*User, error) { // Real database query}
// Mock implementation for teststype 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 mockfunc TestUserService(t *testing.T) { mock := &MockUserRepository{ GetUserFunc: func(id string) (*User, error) { if id == "123" { return &User{ID: "123", Name: "Alice"}, nil } return nil, ErrNotFound }, }
service := NewUserService(mock)
user, err := service.GetUserProfile("123") if err != nil { t.Fatalf("unexpected error: %v", err) } if user.Name != "Alice" { t.Errorf("got name %q; want %q", user.Name, "Alice") }}Benchmarks
Basic Benchmarks
go
func BenchmarkProcess(b *testing.B) { data := generateTestData(1000) b.ResetTimer() // Don't count setup time
for i := 0; i < b.N; i++ { Process(data) }}
// Run: go test -bench=BenchmarkProcess -benchmem// Output: BenchmarkProcess-8 10000 105234 ns/op 4096 B/op 10 allocs/opBenchmark with Different Sizes
go
func BenchmarkSort(b *testing.B) { sizes := []int{100, 1000, 10000, 100000}
for _, size := range sizes { b.Run(fmt.Sprintf("size=%d", size), func(b *testing.B) { data := generateRandomSlice(size) b.ResetTimer()
for i := 0; i < b.N; i++ { // Make a copy to avoid sorting already sorted data tmp := make([]int, len(data)) copy(tmp, data) sort.Ints(tmp) } }) }}Memory Allocation Benchmarks
go
func BenchmarkStringConcat(b *testing.B) { parts := []string{"hello", "world", "foo", "bar", "baz"}
b.Run("plus", func(b *testing.B) { for i := 0; i < b.N; i++ { var s string for _, p := range parts { s += p } _ = s } })
b.Run("builder", func(b *testing.B) { for i := 0; i < b.N; i++ { var sb strings.Builder for _, p := range parts { sb.WriteString(p) } _ = sb.String() } })
b.Run("join", func(b *testing.B) { for i := 0; i < b.N; i++ { _ = strings.Join(parts, "") } })}Fuzzing (Go 1.18+)
Basic Fuzz Test
go
func FuzzParseJSON(f *testing.F) { // Add seed corpus f.Add(`{"name": "test"}`) f.Add(`{"count": 123}`) f.Add(`[]`) f.Add(`""`)
f.Fuzz(func(t *testing.T, input string) { var result map[string]interface{} err := json.Unmarshal([]byte(input), &result)
if err != nil { // Invalid JSON is expected for random input return }
// If parsing succeeded, re-encoding should work _, err = json.Marshal(result) if err != nil { t.Errorf("Marshal failed after successful Unmarshal: %v", err) } })}
// Run: go test -fuzz=FuzzParseJSON -fuzztime=30sFuzz Test with Multiple Inputs
go
func FuzzCompare(f *testing.F) { f.Add("hello", "world") f.Add("", "") f.Add("abc", "abc")
f.Fuzz(func(t *testing.T, a, b string) { result := Compare(a, b)
// Property: Compare(a, a) should always equal 0 if a == b && result != 0 { t.Errorf("Compare(%q, %q) = %d; want 0", a, b, result) }
// Property: Compare(a, b) and Compare(b, a) should have opposite signs reverse := Compare(b, a) if (result > 0 && reverse >= 0) || (result < 0 && reverse <= 0) { if result != 0 || reverse != 0 { t.Errorf("Compare(%q, %q) = %d, Compare(%q, %q) = %d; inconsistent", a, b, result, b, a, reverse) } } })}Test Coverage
Running Coverage
bash
# Basic coveragego test -cover ./...
# Generate coverage profilego test -coverprofile=coverage.out ./...
# View coverage in browsergo tool cover -html=coverage.out
# View coverage by functiongo tool cover -func=coverage.out
# Coverage with race detectiongo test -race -coverprofile=coverage.out ./...Coverage Targets
| Code Type | Target |
|---|---|
| Critical business logic | 100% |
| Public APIs | 90%+ |
| General code | 80%+ |
| Generated code | Exclude |
Excluding Generated Code from Coverage
go
//go:generate mockgen -source=interface.go -destination=mock_interface.go
// In coverage profile, exclude with build tags:// go test -cover -tags=!generate ./...HTTP Handler Testing
go
func TestHealthHandler(t *testing.T) { // Create request req := httptest.NewRequest(http.MethodGet, "/health", nil) w := httptest.NewRecorder()
// Call handler HealthHandler(w, req)
// Check response resp := w.Result() defer resp.Body.Close()
if resp.StatusCode != http.StatusOK { t.Errorf("got status %d; want %d", resp.StatusCode, http.StatusOK) }
body, _ := io.ReadAll(resp.Body) if string(body) != "OK" { t.Errorf("got body %q; want %q", body, "OK") }}
func TestAPIHandler(t *testing.T) { tests := []struct { name string method string path string body string wantStatus int wantBody string }{ { name: "get user", method: http.MethodGet, path: "/users/123", wantStatus: http.StatusOK, wantBody: `{"id":"123","name":"Alice"}`, }, { name: "not found", method: http.MethodGet, path: "/users/999", wantStatus: http.StatusNotFound, }, { name: "create user", method: http.MethodPost, path: "/users", body: `{"name":"Bob"}`, wantStatus: http.StatusCreated, }, }
handler := NewAPIHandler()
for _, tt := range tests { t.Run(tt.name, func(t *testing.T) { var body io.Reader if tt.body != "" { body = strings.NewReader(tt.body) }
req := httptest.NewRequest(tt.method, tt.path, body) req.Header.Set("Content-Type", "application/json") w := httptest.NewRecorder()
handler.ServeHTTP(w, req)
if w.Code != tt.wantStatus { t.Errorf("got status %d; want %d", w.Code, tt.wantStatus) }
if tt.wantBody != "" && w.Body.String() != tt.wantBody { t.Errorf("got body %q; want %q", w.Body.String(), tt.wantBody) } }) }}Testing Commands
bash
# Run all testsgo test ./...
# Run tests with verbose outputgo test -v ./...
# Run specific testgo test -run TestAdd ./...
# Run tests matching patterngo test -run "TestUser/Create" ./...
# Run tests with race detectorgo test -race ./...
# Run tests with coveragego test -cover -coverprofile=coverage.out ./...
# Run short tests onlygo test -short ./...
# Run tests with timeoutgo test -timeout 30s ./...
# Run benchmarksgo test -bench=. -benchmem ./...
# Run fuzzinggo test -fuzz=FuzzParse -fuzztime=30s ./...
# Count test runs (for flaky test detection)go test -count=10 ./...Best Practices
DO:
- Write tests FIRST (TDD)
- Use table-driven tests for comprehensive coverage
- Test behavior, not implementation
- Use
t.Helper()in helper functions - Use
t.Parallel()for independent tests - Clean up resources with
t.Cleanup() - Use meaningful test names that describe the scenario
DON'T:
- Test private functions directly (test through public API)
- Use
time.Sleep()in tests (use channels or conditions) - Ignore flaky tests (fix or remove them)
- Mock everything (prefer integration tests when possible)
- Skip error path testing
Integration with CI/CD
yaml
# GitHub Actions exampletest: runs-on: ubuntu-latest steps: - uses: actions/checkout@v4 - uses: actions/setup-go@v5 with: go-version: '1.22'
- name: Run tests run: go test -race -coverprofile=coverage.out ./...
- name: Check coverage run: | go tool cover -func=coverage.out | grep total | awk '{print $3}' | \ awk -F'%' '{if ($1 < 80) exit 1}'Remember: Tests are documentation. They show how your code is meant to be used. Write them clearly and keep them up to date.
