Testing with godi

One of the greatest benefits of dependency injection is how it transforms testing. This tutorial shows you how to write comprehensive tests for applications using godi.

Why DI Makes Testing Better

Without DI, testing often involves:

Complex setup with real databases
Slow tests due to external dependencies
Brittle tests that fail due to network issues
Difficulty isolating components

With godi:

Easy mock injection
Fast, isolated unit tests
Reliable and repeatable
Clear test boundaries

Setting Up

We’ll test the blog API from the Web Application Tutorial. First, create a test utilities package:

mkdir -p internal/testutil

Step 1: Create Test Utilities

Create internal/testutil/di.go:

package testutil

import (
    "testing"
    "github.com/junioryono/godi"
    "github.com/stretchr/testify/require"
)

// TestProvider creates a DI provider for tests
type TestProvider struct {
    provider godi.ServiceProvider
    t        *testing.T
}

// NewTestProvider creates a new test provider
func NewTestProvider(t *testing.T, opts ...Option) *TestProvider {
    services := godi.NewServiceCollection()

    // Apply options
    cfg := &config{
        services: services,
    }
    for _, opt := range opts {
        opt(cfg)
    }

    // Build provider
    provider, err := services.BuildServiceProvider()
    require.NoError(t, err)

    // Auto-cleanup
    t.Cleanup(func() {
        provider.Close()
    })

    return &TestProvider{
        provider: provider,
        t:        t,
    }
}

// Provider returns the underlying service provider
func (tp *TestProvider) Provider() godi.ServiceProvider {
    return tp.provider
}

// Resolve resolves a service with automatic error checking
func (tp *TestProvider) Resolve(service interface{}) {
    err := tp.provider.Invoke(func(svc interface{}) {
        // Use reflection to set the service
        reflect.ValueOf(service).Elem().Set(reflect.ValueOf(svc))
    })
    require.NoError(tp.t, err)
}

// WithScope creates a test scope
func (tp *TestProvider) WithScope(fn func(scope godi.Scope)) {
    scope := tp.provider.CreateScope(context.Background())
    defer scope.Close()
    fn(scope)
}

// Option configures the test provider
type Option func(*config)

type config struct {
    services godi.ServiceCollection
}

// WithService adds a service to the test container
func WithService(lifetime godi.ServiceLifetime, constructor interface{}) Option {
    return func(c *config) {
        switch lifetime {
        case godi.Singleton:
            c.services.AddSingleton(constructor)
        case godi.Scoped:
            c.services.AddScoped(constructor)
        case godi.Transient:
            c.services.AddTransient(constructor)
        }
    }
}

// WithMock adds a mock service
func WithMock(serviceType reflect.Type, mock interface{}) Option {
    return func(c *config) {
        c.services.AddSingleton(func() interface{} {
            return mock
        })
    }
}

Step 2: Create Mocks

Create internal/mocks/repositories.go:

package mocks

import (
    "context"
    "errors"
    "sync"

    "blog-api/internal/models"
)

// MockUserRepository is a mock implementation of UserRepository
type MockUserRepository struct {
    mu      sync.RWMutex
    users   map[string]*models.User
    calls   []string
    err     error // Can be set to simulate errors
}

func NewMockUserRepository() *MockUserRepository {
    return &MockUserRepository{
        users: make(map[string]*models.User),
    }
}

// WithUsers sets initial users
func (m *MockUserRepository) WithUsers(users ...*models.User) *MockUserRepository {
    for _, user := range users {
        m.users[user.ID] = user
    }
    return m
}

// WithError simulates an error
func (m *MockUserRepository) WithError(err error) *MockUserRepository {
    m.err = err
    return m
}

func (m *MockUserRepository) Create(ctx context.Context, user *models.User) error {
    m.mu.Lock()
    defer m.mu.Unlock()

    m.calls = append(m.calls, "Create")

    if m.err != nil {
        return m.err
    }

    if user.ID == "" {
        user.ID = "test-id"
    }

    m.users[user.ID] = user
    return nil
}

func (m *MockUserRepository) GetByID(ctx context.Context, id string) (*models.User, error) {
    m.mu.RLock()
    defer m.mu.RUnlock()

    m.calls = append(m.calls, "GetByID")

    if m.err != nil {
        return nil, m.err
    }

    user, exists := m.users[id]
    if !exists {
        return nil, errors.New("not found")
    }

    return user, nil
}

func (m *MockUserRepository) GetByUsername(ctx context.Context, username string) (*models.User, error) {
    m.mu.RLock()
    defer m.mu.RUnlock()

    m.calls = append(m.calls, "GetByUsername")

    if m.err != nil {
        return nil, m.err
    }

    for _, user := range m.users {
        if user.Username == username {
            return user, nil
        }
    }

    return nil, errors.New("not found")
}

// GetCalls returns the method calls made
func (m *MockUserRepository) GetCalls() []string {
    m.mu.RLock()
    defer m.mu.RUnlock()

    calls := make([]string, len(m.calls))
    copy(calls, m.calls)
    return calls
}

// MockLogger for testing
type MockLogger struct {
    mu       sync.Mutex
    messages []LogMessage
}

type LogMessage struct {
    Level   string
    Message string
    Args    []interface{}
}

func NewMockLogger() *MockLogger {
    return &MockLogger{}
}

func (l *MockLogger) Info(msg string, args ...interface{}) {
    l.mu.Lock()
    defer l.mu.Unlock()

    l.messages = append(l.messages, LogMessage{
        Level:   "INFO",
        Message: msg,
        Args:    args,
    })
}

func (l *MockLogger) Error(msg string, err error, args ...interface{}) {
    l.mu.Lock()
    defer l.mu.Unlock()

    l.messages = append(l.messages, LogMessage{
        Level:   "ERROR",
        Message: msg,
        Args:    append([]interface{}{err}, args...),
    })
}

func (l *MockLogger) GetMessages() []LogMessage {
    l.mu.Lock()
    defer l.mu.Unlock()

    messages := make([]LogMessage, len(l.messages))
    copy(messages, l.messages)
    return messages
}

Step 3: Unit Testing Services

Create internal/services/auth_test.go:

package services_test

import (
    "context"
    "testing"

    "blog-api/internal/config"
    "blog-api/internal/models"
    "blog-api/internal/mocks"
    "blog-api/internal/services"

    "github.com/junioryono/godi"
    "github.com/stretchr/testify/assert"
    "github.com/stretchr/testify/require"
)

func TestAuthService_Register(t *testing.T) {
    tests := []struct {
        name      string
        setup     func(*mocks.MockUserRepository)
        request   *models.RegisterRequest
        wantErr   bool
        errMsg    string
        checkUser func(*testing.T, *models.User)
    }{
        {
            name: "successful registration",
            setup: func(repo *mocks.MockUserRepository) {
                // Empty repo - no existing users
            },
            request: &models.RegisterRequest{
                Username: "newuser",
                Email:    "new@example.com",
                Password: "password123",
            },
            wantErr: false,
            checkUser: func(t *testing.T, user *models.User) {
                assert.Equal(t, "newuser", user.Username)
                assert.Equal(t, "new@example.com", user.Email)
                assert.NotEmpty(t, user.ID)
                assert.NotEqual(t, "password123", user.PasswordHash) // Should be hashed
            },
        },
        {
            name: "duplicate username",
            setup: func(repo *mocks.MockUserRepository) {
                repo.WithUsers(&models.User{
                    ID:       "existing",
                    Username: "newuser",
                    Email:    "other@example.com",
                })
            },
            request: &models.RegisterRequest{
                Username: "newuser",
                Email:    "new@example.com",
                Password: "password123",
            },
            wantErr: true,
            errMsg:  "user already exists",
        },
        {
            name: "duplicate email",
            setup: func(repo *mocks.MockUserRepository) {
                repo.WithUsers(&models.User{
                    ID:       "existing",
                    Username: "other",
                    Email:    "new@example.com",
                })
            },
            request: &models.RegisterRequest{
                Username: "newuser",
                Email:    "new@example.com",
                Password: "password123",
            },
            wantErr: true,
            errMsg:  "user already exists",
        },
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            // Setup DI container
            services := godi.NewServiceCollection()

            // Register mocks
            mockRepo := mocks.NewMockUserRepository()
            if tt.setup != nil {
                tt.setup(mockRepo)
            }

            services.AddSingleton(func() repositories.UserRepository {
                return mockRepo
            })
            services.AddSingleton(func() *config.Config {
                return &config.Config{
                    JWTSecret:     "test-secret",
                    JWTExpiration: time.Hour,
                }
            })
            services.AddScoped(services.NewAuthService)

            // Build provider
            provider, err := services.BuildServiceProvider()
            require.NoError(t, err)
            defer provider.Close()

            // Create scope
            scope := provider.CreateScope(context.Background())
            defer scope.Close()

            // Resolve service
            authService, err := godi.Resolve[services.AuthService](scope.ServiceProvider())
            require.NoError(t, err)

            // Execute test
            resp, err := authService.Register(context.Background(), tt.request)

            // Check results
            if tt.wantErr {
                assert.Error(t, err)
                if tt.errMsg != "" {
                    assert.Contains(t, err.Error(), tt.errMsg)
                }
                assert.Nil(t, resp)
            } else {
                assert.NoError(t, err)
                assert.NotNil(t, resp)
                assert.NotEmpty(t, resp.Token)

                if tt.checkUser != nil {
                    tt.checkUser(t, resp.User)
                }

                // Verify user was saved
                savedUser, _ := mockRepo.GetByID(context.Background(), resp.User.ID)
                assert.NotNil(t, savedUser)
            }

            // Verify repository calls
            calls := mockRepo.GetCalls()
            assert.Contains(t, calls, "GetByUsername")
            assert.Contains(t, calls, "GetByEmail")
            if !tt.wantErr {
                assert.Contains(t, calls, "Create")
            }
        })
    }
}

func TestAuthService_Login(t *testing.T) {
    // Create a test user with hashed password
    hashedPassword, _ := bcrypt.GenerateFromPassword([]byte("correct-password"), bcrypt.DefaultCost)
    testUser := &models.User{
        ID:           "user-123",
        Username:     "testuser",
        Email:        "test@example.com",
        PasswordHash: string(hashedPassword),
    }

    tests := []struct {
        name    string
        setup   func(*mocks.MockUserRepository)
        request *models.LoginRequest
        wantErr bool
        errMsg  string
    }{
        {
            name: "successful login",
            setup: func(repo *mocks.MockUserRepository) {
                repo.WithUsers(testUser)
            },
            request: &models.LoginRequest{
                Username: "testuser",
                Password: "correct-password",
            },
            wantErr: false,
        },
        {
            name: "wrong password",
            setup: func(repo *mocks.MockUserRepository) {
                repo.WithUsers(testUser)
            },
            request: &models.LoginRequest{
                Username: "testuser",
                Password: "wrong-password",
            },
            wantErr: true,
            errMsg:  "invalid credentials",
        },
        {
            name: "user not found",
            setup: func(repo *mocks.MockUserRepository) {
                // Empty repo
            },
            request: &models.LoginRequest{
                Username: "nonexistent",
                Password: "password",
            },
            wantErr: true,
            errMsg:  "invalid credentials",
        },
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            // Use test helper
            tp := testutil.NewTestProvider(t,
                testutil.WithService(godi.Singleton, func() repositories.UserRepository {
                    repo := mocks.NewMockUserRepository()
                    if tt.setup != nil {
                        tt.setup(repo)
                    }
                    return repo
                }),
                testutil.WithService(godi.Singleton, func() *config.Config {
                    return &config.Config{
                        JWTSecret:     "test-secret",
                        JWTExpiration: time.Hour,
                    }
                }),
                testutil.WithService(godi.Scoped, services.NewAuthService),
            )

            tp.WithScope(func(scope godi.Scope) {
                authService, err := godi.Resolve[services.AuthService](scope.ServiceProvider())
                require.NoError(t, err)

                resp, err := authService.Login(context.Background(), tt.request)

                if tt.wantErr {
                    assert.Error(t, err)
                    if tt.errMsg != "" {
                        assert.Contains(t, err.Error(), tt.errMsg)
                    }
                } else {
                    assert.NoError(t, err)
                    assert.NotNil(t, resp)
                    assert.NotEmpty(t, resp.Token)
                    assert.Equal(t, testUser.ID, resp.User.ID)

                    // Verify token is valid
                    userID, err := authService.ValidateToken(resp.Token)
                    assert.NoError(t, err)
                    assert.Equal(t, testUser.ID, userID)
                }
            })
        })
    }
}

Step 4: Integration Testing

Create internal/handlers/auth_integration_test.go:

package handlers_test

import (
    "bytes"
    "encoding/json"
    "net/http"
    "net/http/httptest"
    "testing"

    "blog-api/internal/config"
    "blog-api/internal/handlers"
    "blog-api/internal/models"
    "blog-api/internal/repositories"
    "blog-api/internal/services"

    "github.com/gorilla/mux"
    "github.com/junioryono/godi"
    "github.com/stretchr/testify/assert"
    "github.com/stretchr/testify/require"
)

func TestAuthHandler_Integration(t *testing.T) {
    // Setup DI container with real implementations
    services := godi.NewServiceCollection()

    // Use in-memory implementations for integration tests
    services.AddSingleton(repositories.NewInMemoryUserRepository)
    services.AddSingleton(func() *config.Config {
        return &config.Config{
            JWTSecret:     "test-integration-secret",
            JWTExpiration: time.Hour,
        }
    })
    services.AddScoped(services.NewAuthService)
    services.AddScoped(handlers.NewAuthHandler)

    provider, err := services.BuildServiceProvider()
    require.NoError(t, err)
    defer provider.Close()

    // Setup router
    router := mux.NewRouter()
    router.Use(handlers.DIMiddleware(provider))

    router.HandleFunc("/auth/register", func(w http.ResponseWriter, r *http.Request) {
        scope := handlers.GetScope(r.Context())
        handler, _ := godi.Resolve[*handlers.AuthHandler](scope.ServiceProvider())
        handler.Register(w, r)
    }).Methods("POST")

    router.HandleFunc("/auth/login", func(w http.ResponseWriter, r *http.Request) {
        scope := handlers.GetScope(r.Context())
        handler, _ := godi.Resolve[*handlers.AuthHandler](scope.ServiceProvider())
        handler.Login(w, r)
    }).Methods("POST")

    // Test server
    server := httptest.NewServer(router)
    defer server.Close()

    t.Run("full auth flow", func(t *testing.T) {
        // Register
        registerReq := models.RegisterRequest{
            Username: "integrationuser",
            Email:    "integration@test.com",
            Password: "testpass123",
        }

        body, _ := json.Marshal(registerReq)
        resp, err := http.Post(
            server.URL+"/auth/register",
            "application/json",
            bytes.NewReader(body),
        )
        require.NoError(t, err)
        defer resp.Body.Close()

        assert.Equal(t, http.StatusOK, resp.StatusCode)

        var registerResp models.AuthResponse
        err = json.NewDecoder(resp.Body).Decode(&registerResp)
        require.NoError(t, err)

        assert.NotEmpty(t, registerResp.Token)
        assert.Equal(t, "integrationuser", registerResp.User.Username)

        // Login with same credentials
        loginReq := models.LoginRequest{
            Username: "integrationuser",
            Password: "testpass123",
        }

        body, _ = json.Marshal(loginReq)
        resp, err = http.Post(
            server.URL+"/auth/login",
            "application/json",
            bytes.NewReader(body),
        )
        require.NoError(t, err)
        defer resp.Body.Close()

        assert.Equal(t, http.StatusOK, resp.StatusCode)

        var loginResp models.AuthResponse
        err = json.NewDecoder(resp.Body).Decode(&loginResp)
        require.NoError(t, err)

        assert.NotEmpty(t, loginResp.Token)
        assert.Equal(t, registerResp.User.ID, loginResp.User.ID)
    })

    t.Run("duplicate registration", func(t *testing.T) {
        // First registration
        registerReq := models.RegisterRequest{
            Username: "duplicate",
            Email:    "duplicate@test.com",
            Password: "testpass123",
        }

        body, _ := json.Marshal(registerReq)
        resp, err := http.Post(
            server.URL+"/auth/register",
            "application/json",
            bytes.NewReader(body),
        )
        require.NoError(t, err)
        resp.Body.Close()

        assert.Equal(t, http.StatusOK, resp.StatusCode)

        // Duplicate registration
        resp, err = http.Post(
            server.URL+"/auth/register",
            "application/json",
            bytes.NewReader(body),
        )
        require.NoError(t, err)
        defer resp.Body.Close()

        assert.Equal(t, http.StatusConflict, resp.StatusCode)
    })
}

Step 5: Testing Scoped Services

Create internal/services/scope_test.go:

package services_test

import (
    "context"
    "sync"
    "testing"

    "blog-api/internal/services"

    "github.com/junioryono/godi"
    "github.com/stretchr/testify/assert"
    "github.com/stretchr/testify/require"
)

// Service that tracks its instances
type InstanceTracker struct {
    ID       string
    Created  time.Time
}

type TrackedService struct {
    instance *InstanceTracker
}

func NewTrackedService() *TrackedService {
    return &TrackedService{
        instance: &InstanceTracker{
            ID:      uuid.New().String(),
            Created: time.Now(),
        },
    }
}

func (s *TrackedService) GetInstance() *InstanceTracker {
    return s.instance
}

func TestScopedLifetime(t *testing.T) {
    services := godi.NewServiceCollection()

    // Register as scoped
    services.AddScoped(NewTrackedService)

    provider, err := services.BuildServiceProvider()
    require.NoError(t, err)
    defer provider.Close()

    t.Run("same instance within scope", func(t *testing.T) {
        scope := provider.CreateScope(context.Background())
        defer scope.Close()

        // Resolve multiple times
        svc1, err := godi.Resolve[*TrackedService](scope.ServiceProvider())
        require.NoError(t, err)

        svc2, err := godi.Resolve[*TrackedService](scope.ServiceProvider())
        require.NoError(t, err)

        // Should be same instance
        assert.Equal(t, svc1.GetInstance().ID, svc2.GetInstance().ID)
        assert.Same(t, svc1, svc2)
    })

    t.Run("different instances across scopes", func(t *testing.T) {
        scope1 := provider.CreateScope(context.Background())
        defer scope1.Close()

        scope2 := provider.CreateScope(context.Background())
        defer scope2.Close()

        svc1, _ := godi.Resolve[*TrackedService](scope1.ServiceProvider())
        svc2, _ := godi.Resolve[*TrackedService](scope2.ServiceProvider())

        // Should be different instances
        assert.NotEqual(t, svc1.GetInstance().ID, svc2.GetInstance().ID)
        assert.NotSame(t, svc1, svc2)
    })

    t.Run("concurrent scope resolution", func(t *testing.T) {
        const numGoroutines = 100
        instances := make(map[string]bool)
        var mu sync.Mutex
        var wg sync.WaitGroup

        wg.Add(numGoroutines)

        for i := 0; i < numGoroutines; i++ {
            go func() {
                defer wg.Done()

                scope := provider.CreateScope(context.Background())
                defer scope.Close()

                svc, err := godi.Resolve[*TrackedService](scope.ServiceProvider())
                require.NoError(t, err)

                mu.Lock()
                instances[svc.GetInstance().ID] = true
                mu.Unlock()
            }()
        }

        wg.Wait()

        // Should have created numGoroutines different instances
        assert.Equal(t, numGoroutines, len(instances))
    })
}

// Test disposal of scoped services
type DisposableService struct {
    ID       string
    disposed bool
    mu       sync.Mutex
}

func NewDisposableService() *DisposableService {
    return &DisposableService{
        ID: uuid.New().String(),
    }
}

func (s *DisposableService) Close() error {
    s.mu.Lock()
    defer s.mu.Unlock()

    if s.disposed {
        return errors.New("already disposed")
    }

    s.disposed = true
    return nil
}

func (s *DisposableService) IsDisposed() bool {
    s.mu.Lock()
    defer s.mu.Unlock()
    return s.disposed
}

func TestScopeDisposal(t *testing.T) {
    services := godi.NewServiceCollection()

    // Track created services
    var createdServices []*DisposableService
    var mu sync.Mutex

    services.AddScoped(func() *DisposableService {
        svc := NewDisposableService()

        mu.Lock()
        createdServices = append(createdServices, svc)
        mu.Unlock()

        return svc
    })

    provider, err := services.BuildServiceProvider()
    require.NoError(t, err)
    defer provider.Close()

    t.Run("services disposed with scope", func(t *testing.T) {
        scope := provider.CreateScope(context.Background())

        // Create service
        svc, err := godi.Resolve[*DisposableService](scope.ServiceProvider())
        require.NoError(t, err)

        assert.False(t, svc.IsDisposed())

        // Close scope
        err = scope.Close()
        require.NoError(t, err)

        // Service should be disposed
        assert.True(t, svc.IsDisposed())
    })

    t.Run("disposal order LIFO", func(t *testing.T) {
        // Clear tracking
        mu.Lock()
        createdServices = nil
        mu.Unlock()

        scope := provider.CreateScope(context.Background())

        // Create multiple services
        const numServices = 5
        for i := 0; i < numServices; i++ {
            _, err := godi.Resolve[*DisposableService](scope.ServiceProvider())
            require.NoError(t, err)
        }

        // Track disposal order
        var disposalOrder []string
        for _, svc := range createdServices {
            id := svc.ID
            originalClose := svc.Close
            svc.Close = func() error {
                disposalOrder = append(disposalOrder, id)
                return originalClose()
            }
        }

        // Close scope
        scope.Close()

        // Verify LIFO order
        assert.Equal(t, numServices, len(disposalOrder))
        for i := 0; i < numServices; i++ {
            expectedIdx := numServices - 1 - i
            assert.Equal(t, createdServices[expectedIdx].ID, disposalOrder[i])
        }
    })
}

Step 6: Testing Best Practices

Create internal/testutil/assertions.go:

package testutil

import (
    "testing"
    "github.com/stretchr/testify/assert"
)

// AssertErrorType checks if an error is of a specific type
func AssertErrorType[T error](t *testing.T, err error) {
    t.Helper()

    var target T
    assert.ErrorAs(t, err, &target, "expected error type %T", target)
}

// AssertServiceRegistered verifies a service is registered
func AssertServiceRegistered[T any](t *testing.T, provider godi.ServiceProvider) {
    t.Helper()

    _, err := godi.Resolve[T](provider)
    assert.NoError(t, err, "service %T should be registered", *new(T))
}

// AssertServiceNotRegistered verifies a service is not registered
func AssertServiceNotRegistered[T any](t *testing.T, provider godi.ServiceProvider) {
    t.Helper()

    _, err := godi.Resolve[T](provider)
    assert.Error(t, err, "service %T should not be registered", *new(T))
}

Create test table helper internal/testutil/table.go:

package testutil

import (
    "context"
    "testing"

    "github.com/junioryono/godi"
)

// ServiceTest defines a table-driven test for services
type ServiceTest struct {
    Name      string
    Setup     func(godi.ServiceCollection)
    Test      func(context.Context, godi.ServiceProvider) error
    WantError bool
    ErrorMsg  string
}

// RunServiceTests executes table-driven tests
func RunServiceTests(t *testing.T, tests []ServiceTest) {
    for _, tt := range tests {
        t.Run(tt.Name, func(t *testing.T) {
            // Create container
            services := godi.NewServiceCollection()

            // Apply setup
            if tt.Setup != nil {
                tt.Setup(services)
            }

            // Build provider
            provider, err := services.BuildServiceProvider()
            if err != nil {
                t.Fatalf("failed to build provider: %v", err)
            }
            defer provider.Close()

            // Run test
            ctx := context.Background()
            err = tt.Test(ctx, provider)

            // Check result
            if tt.WantError {
                assert.Error(t, err)
                if tt.ErrorMsg != "" {
                    assert.Contains(t, err.Error(), tt.ErrorMsg)
                }
            } else {
                assert.NoError(t, err)
            }
        })
    }
}

Step 7: Benchmark Tests

Create internal/services/benchmark_test.go:

package services_test

import (
    "context"
    "testing"

    "blog-api/internal/config"
    "blog-api/internal/mocks"
    "blog-api/internal/repositories"
    "blog-api/internal/services"

    "github.com/junioryono/godi"
)

func BenchmarkServiceResolution(b *testing.B) {
    services := godi.NewServiceCollection()

    // Register services
    services.AddSingleton(func() repositories.UserRepository {
        return mocks.NewMockUserRepository()
    })
    services.AddSingleton(func() *config.Config {
        return &config.Config{
            JWTSecret:     "bench-secret",
            JWTExpiration: time.Hour,
        }
    })
    services.AddScoped(services.NewAuthService)

    provider, _ := services.BuildServiceProvider()
    defer provider.Close()

    b.Run("singleton resolution", func(b *testing.B) {
        b.ResetTimer()
        for i := 0; i < b.N; i++ {
            _, err := godi.Resolve[*config.Config](provider)
            if err != nil {
                b.Fatal(err)
            }
        }
    })

    b.Run("scoped resolution", func(b *testing.B) {
        scope := provider.CreateScope(context.Background())
        defer scope.Close()

        b.ResetTimer()
        for i := 0; i < b.N; i++ {
            _, err := godi.Resolve[services.AuthService](scope.ServiceProvider())
            if err != nil {
                b.Fatal(err)
            }
        }
    })

    b.Run("scope creation and disposal", func(b *testing.B) {
        b.ResetTimer()
        for i := 0; i < b.N; i++ {
            scope := provider.CreateScope(context.Background())
            godi.Resolve[services.AuthService](scope.ServiceProvider())
            scope.Close()
        }
    })
}

func BenchmarkConcurrentResolution(b *testing.B) {
    services := godi.NewServiceCollection()

    services.AddSingleton(func() repositories.UserRepository {
        return mocks.NewMockUserRepository()
    })
    services.AddSingleton(func() *config.Config {
        return &config.Config{}
    })
    services.AddScoped(services.NewAuthService)

    provider, _ := services.BuildServiceProvider()
    defer provider.Close()

    b.RunParallel(func(pb *testing.PB) {
        for pb.Next() {
            scope := provider.CreateScope(context.Background())
            godi.Resolve[services.AuthService](scope.ServiceProvider())
            scope.Close()
        }
    })
}

Testing Strategies

1. Unit Testing with Mocks

Mock external dependencies
Test business logic in isolation
Fast and reliable

2. Integration Testing

Use in-memory implementations
Test component interactions
Verify API contracts

3. End-to-End Testing

Real implementations where possible
Test complete user flows
Slower but comprehensive

4. Test Organization

internal/
├── services/
│   ├── auth.go
│   ├── auth_test.go          # Unit tests
│   └── auth_integration_test.go
├── handlers/
│   ├── auth.go
│   └── auth_test.go          # Handler tests
├── mocks/                    # Shared mocks
│   ├── repositories.go
│   └── services.go
└── testutil/                 # Test utilities
    ├── di.go
    ├── assertions.go
    └── fixtures.go

Key Testing Benefits with godi

1. Easy Mock Injection

// Replace real service with mock
services.AddSingleton(func() UserRepository {
    return &MockUserRepository{
        users: testUsers,
    }
})

2. Isolated Test Environments

// Each test gets fresh container
func TestFeature(t *testing.T) {
    provider := createTestProvider(t)
    // Test in isolation
}

3. Parallel Testing

// Safe parallel tests with separate containers
func TestParallel(t *testing.T) {
    t.Parallel()

    provider := createTestProvider(t)
    // Each test has its own instances
}

4. Test-Specific Configuration

// Override configuration for tests
services.AddSingleton(func() *Config {
    return &Config{
        Environment: "test",
        LogLevel:    "debug",
    }
})

Common Testing Patterns

Factory Pattern for Test Data

func NewTestUser(opts ...func(*models.User)) *models.User {
    user := &models.User{
        ID:       uuid.New().String(),
        Username: "testuser",
        Email:    "test@example.com",
    }

    for _, opt := range opts {
        opt(user)
    }

    return user
}

// Usage
user := NewTestUser(
    WithUsername("custom"),
    WithEmail("custom@test.com"),
)

Test Fixtures

type Fixtures struct {
    Users    []*models.User
    Posts    []*models.Post
    Comments []*models.Comment
}

func LoadFixtures(t *testing.T, provider godi.ServiceProvider) *Fixtures {
    // Load test data
    return &Fixtures{
        Users: loadTestUsers(t, provider),
        Posts: loadTestPosts(t, provider),
    }
}

Cleanup Helpers

func TestWithCleanup(t *testing.T) {
    provider := createTestProvider(t)

    // Automatic cleanup
    t.Cleanup(func() {
        provider.Close()
        cleanupTestData()
    })

    // Test code
}

Summary

Testing with godi transforms the testing experience:

Mock injection is trivial
Test isolation is automatic
Parallel tests are safe
Setup/teardown is simplified
Integration tests use same DI pattern

The combination of dependency injection and Go’s testing package creates a powerful testing environment that encourages comprehensive test coverage and maintainable test code.