Generating Mocks

This skill guides you through generating and managing mock implementations using mockery.

Quick Commands

make mock-gen      # Generate all mocks
make mock-clean    # Remove all generated mocks

Mockery Configuration

Configuration is in .mockery.yaml:

with-expecter: true    # Enable EXPECT() style assertions
testonly: false        # Don't add //go:build test constraint
all: false             # Don't auto-generate for all interfaces
packages:
  app/internal/shared/domain/repository:
    interfaces:
      UserRepository:
        config:
          dir: internal/mocks/repository
          outpkg: mocks
  app/internal/features/auth/usecase:
    interfaces:
      AuthUsecase:
        config:
          dir: internal/mocks/usecase
          outpkg: mocks

Adding a New Interface to Mock

Step 1: Define the Interface

Create your interface in the appropriate package:

// internal/features/product/usecase/product_usecase.go
package usecase

import "app/internal/features/product/delivery/http/dto"

type ProductUsecase interface {
    CreateProduct(req *dto.CreateProductRequest) (*dto.ProductResponse, error)
    GetProductByID(id string) (*dto.ProductResponse, error)
    ListProducts(page, perPage int) ([]dto.ProductResponse, int64, error)
    UpdateProduct(id string, req *dto.UpdateProductRequest) (*dto.ProductResponse, error)
    DeleteProduct(id string) error
}

Step 2: Add to .mockery.yaml

Add the interface to .mockery.yaml:

packages:
  # ... existing packages ...

  app/internal/features/product/usecase:
    interfaces:
      ProductUsecase:
        config:
          dir: internal/mocks/usecase
          outpkg: mocks

Step 3: Generate Mocks

make mock-gen

This creates: internal/mocks/usecase/mock_ProductUsecase.go

Step 4: Use the Mock in Tests

package handler

import (
    mocks "app/internal/mocks/usecase"
    "testing"

    "github.com/stretchr/testify/assert"
)

func TestProductHandler_CreateProduct(t *testing.T) {
    // Create mock
    mockUsecase := mocks.NewMockProductUsecase(t)

    // Set expectations
    mockUsecase.EXPECT().
        CreateProduct(mock.AnythingOfType("*dto.CreateProductRequest")).
        Return(&dto.ProductResponse{ID: "123"}, nil).
        Once()

    // Use mock in tests...
    handler := NewProductHandler(mockUsecase)

    // ... test code ...

    // Verify expectations
    mockUsecase.AssertExpectations(t)
}

Mock Patterns

Repository Mocks

Repository interfaces are typically in internal/shared/domain/repository/:

packages:
  app/internal/shared/domain/repository:
    interfaces:
      ProductRepository:
        config:
          dir: internal/mocks/repository
          outpkg: mocks

Generated mock: internal/mocks/repository/mock_ProductRepository.go

Use Case Mocks

Use case interfaces are in feature-specific packages:

packages:
  app/internal/features/product/usecase:
    interfaces:
      ProductUsecase:
        config:
          dir: internal/mocks/usecase
          outpkg: mocks

Generated mock: internal/mocks/usecase/mock_ProductUsecase.go

Using Generated Mocks

Basic Expectations

// Exact arguments
mockRepo.EXPECT().
    FindByID("123").
    Return(user, nil).
    Once()

// Any arguments
mockRepo.EXPECT().
    Create(mock.AnythingOfType("*entity.User")).
    Return(nil).
    Once()

// Multiple calls
mockRepo.EXPECT().
    List().
    Return([]entity.User{}, nil).
    Times(3)

Argument Matchers

import "github.com/stretchr/testify/mock"

// Match any value of type
mock.AnythingOfType("string")
mock.AnythingOfType("*entity.User")

// Custom matcher
mockRepo.EXPECT().
    Create(mock.MatchedBy(func(u *entity.User) bool {
        return u.Email == "test@example.com"
    })).
    Return(nil).
    Once()

// Anything (any type)
mockRepo.EXPECT().
    Update(mock.Anything).
    Return(nil).
    Once()

Return Values

// Return single value
mockRepo.EXPECT().
    Delete(userID).
    Return(nil).
    Once()

// Return multiple values
mockRepo.EXPECT().
    FindByEmail("test@example.com").
    Return(user, nil).
    Once()

// Return error
mockRepo.EXPECT().
    FindByID("invalid").
    Return(nil, gorm.ErrRecordNotFound).
    Once()

// Different returns for sequential calls
mockRepo.EXPECT().FindAll().Return([]User{user1}, nil).Once()
mockRepo.EXPECT().FindAll().Return([]User{user1, user2}, nil).Once()

Call Counts

// Called exactly once (default)
mockRepo.EXPECT().Create(user).Return(nil).Once()

// Called exactly N times
mockRepo.EXPECT().Update(user).Return(nil).Times(3)

// Called any number of times (including 0)
mockRepo.EXPECT().GetConfig().Return("config").Maybe()

Complete Example

1. Define Interface

// internal/features/notification/usecase/notification_usecase.go
package usecase

type NotificationUsecase interface {
    SendEmail(to, subject, body string) error
    SendSMS(to, message string) error
}

2. Add to .mockery.yaml

packages:
  app/internal/features/notification/usecase:
    interfaces:
      NotificationUsecase:
        config:
          dir: internal/mocks/usecase
          outpkg: mocks

3. Generate Mock

make mock-gen

4. Use in Test

package usecase

import (
    "app/internal/features/notification/usecase"
    mocks "app/internal/mocks/usecase"
    "testing"

    "github.com/stretchr/testify/assert"
    "github.com/stretchr/testify/mock"
)

func TestUserUsecase_RegisterWithNotification(t *testing.T) {
    // Setup mocks
    mockUserRepo := mocks.NewMockUserRepository(t)
    mockNotification := mocks.NewMockNotificationUsecase(t)

    userUsecase := NewUserUsecase(mockUserRepo, mockNotification)

    // Set expectations
    mockUserRepo.EXPECT().
        Create(mock.AnythingOfType("*entity.User")).
        Return(nil).
        Once()

    mockNotification.EXPECT().
        SendEmail(
            "newuser@example.com",
            "Welcome!",
            mock.AnythingOfType("string"),
        ).
        Return(nil).
        Once()

    // Execute test
    err := userUsecase.Register(&RegisterRequest{
        Email: "newuser@example.com",
    })

    // Assert
    assert.NoError(t, err)
    mockUserRepo.AssertExpectations(t)
    mockNotification.AssertExpectations(t)
}

Regenerating Mocks

When to Regenerate

Run make mock-gen after:

• Adding new methods to an interface
• Changing method signatures
• Removing methods from an interface
• Adding new interfaces to mock

Handling Changes

1. Interface method added: Regenerate mocks, update tests
2. Interface method removed: Regenerate mocks, remove test expectations
3. Method signature changed: Regenerate mocks, update test expectations

# Clean and regenerate all mocks
make mock-clean
make mock-gen

Troubleshooting

Mock Not Found

Problem: undefined: mocks.NewMockUserRepository

Solution:

1. Check interface is in .mockery.yaml
2. Run make mock-gen
3. Check mock file exists in internal/mocks/

Wrong Package Name

Problem: Mock generated with wrong package

Solution: Check outpkg in .mockery.yaml:

config:
  dir: internal/mocks/repository
  outpkg: mocks  # Must be "mocks"

Interface Not Found

Problem: mockery: error: failed to find interface UserRepository

Solution:

1. Verify interface exists and is exported (starts with capital letter)
2. Check package path in .mockery.yaml matches actual package
3. Ensure interface name is spelled correctly

Expectation Not Met

Problem: Test fails with "FAIL: Expected function call but did not find it"

Solution:

1. Ensure method is actually called in code
2. Check argument matchers match actual arguments
3. Use mock.Anything for flexible matching during debugging
4. Add .Maybe() if call is optional

Best Practices

1. Always call AssertExpectations(t) at the end of tests
2. Use specific matchers when possible for better test clarity
3. Mock only what you need - don't set expectations for unused methods
4. Regenerate after interface changes to keep mocks in sync
5. Use Once() explicitly to catch unexpected multiple calls
6. Group related mocks in the same directory structure
7. Keep .mockery.yaml organized with clear package groupings

Mock Directory Structure

internal/mocks/
├── repository/
│   ├── mock_UserRepository.go
│   ├── mock_ProductRepository.go
│   └── mock_OrderRepository.go
└── usecase/
    ├── mock_AuthUsecase.go
    ├── mock_UserUsecase.go
    └── mock_ProductUsecase.go

This structure keeps mocks organized by layer (repository vs usecase) for easy discovery.