gomock and mockery Compared for Mocking in Go Projects

package main

import (
	"context"
	"errors"
	"fmt"
)

var ErrNotFound = errors.New("user not found")

type User struct {
	ID    int
	Email string
	Plan  string
}

type Store interface {
	Get(ctx context.Context, id int) (User, error)
	Save(ctx context.Context, u User) error
	Delete(ctx context.Context, id int) error
}

type Service struct{ store Store }

func NewService(s Store) *Service { return &Service{store: s} }

// Upgrade moves a user to the pro plan and saves it once.
func (s *Service) Upgrade(ctx context.Context, id int) error {
	u, err := s.store.Get(ctx, id)
	if err != nil {
		return fmt.Errorf("upgrade %d: %w", id, err)
	}
	if u.Plan == "pro" {
		return nil
	}
	u.Plan = "pro"
	return s.store.Save(ctx, u)
}

func main() {}

go run go.uber.org/mock/[email protected] -source=users.go -destination=store_mock_test.go -package=main

package main

import (
	"context"
	"errors"
	"os"
	"testing"

	"go.uber.org/mock/gomock"
)

func TestUpgrade(t *testing.T) {
	ctx := context.Background()

	t.Run("saves the pro plan once", func(t *testing.T) {
		ctrl := gomock.NewController(t)
		store := NewMockStore(ctrl)
		store.EXPECT().Get(ctx, 7).Return(User{ID: 7, Plan: "free"}, nil)
		store.EXPECT().Save(ctx, User{ID: 7, Plan: "pro"}).Return(nil).Times(1)

		if err := NewService(store).Upgrade(ctx, 7); err != nil {
			t.Fatal(err)
		}
	})

	t.Run("already pro never saves", func(t *testing.T) {
		ctrl := gomock.NewController(t)
		store := NewMockStore(ctrl)
		store.EXPECT().Get(gomock.Any(), 7).Return(User{ID: 7, Plan: "pro"}, nil)

		if err := NewService(store).Upgrade(ctx, 7); err != nil {
			t.Fatal(err)
		}
	})

	t.Run("not found is wrapped", func(t *testing.T) {
		ctrl := gomock.NewController(t)
		store := NewMockStore(ctrl)
		store.EXPECT().Get(gomock.Any(), 9).Return(User{}, ErrNotFound)

		err := NewService(store).Upgrade(ctx, 9)
		if !errors.Is(err, ErrNotFound) {
			t.Fatalf("got %v", err)
		}
	})

	t.Run("matcher and DoAndReturn", func(t *testing.T) {
		ctrl := gomock.NewController(t)
		store := NewMockStore(ctrl)
		store.EXPECT().Get(gomock.Any(), gomock.Any()).DoAndReturn(
			func(_ context.Context, id int) (User, error) {
				return User{ID: id, Plan: "free"}, nil
			})
		store.EXPECT().Save(gomock.Any(), gomock.Cond(func(u User) bool { return u.Plan == "pro" })).Return(nil)

		if err := NewService(store).Upgrade(ctx, 21); err != nil {
			t.Fatal(err)
		}
	})
}

// Runs only when DEMO is set, to record what a violated expectation prints.
func TestDemoMissingSave(t *testing.T) {
	if os.Getenv("DEMO") == "" {
		t.Skip("demo only")
	}
	ctrl := gomock.NewController(t)
	store := NewMockStore(ctrl)
	store.EXPECT().Get(gomock.Any(), 7).Return(User{ID: 7, Plan: "free"}, nil)
	store.EXPECT().Save(gomock.Any(), User{ID: 7, Plan: "pro"}).Return(nil)
	// The service is never called, so both expectations are unmet.
}

func TestDemoUnexpectedCall(t *testing.T) {
	if os.Getenv("DEMO") == "" {
		t.Skip("demo only")
	}
	ctrl := gomock.NewController(t)
	store := NewMockStore(ctrl)
	store.EXPECT().Get(gomock.Any(), 7).Return(User{ID: 7, Plan: "free"}, nil)
	_ = NewService(store).Upgrade(context.Background(), 7)
}

// Code generated by MockGen. DO NOT EDIT.
// Source: users.go
//
// Generated by this command:
//
//	mockgen -source=users.go -destination=store_mock_test.go -package=main
//

// Package main is a generated GoMock package.
package main

import (
	context "context"
	reflect "reflect"

	gomock "go.uber.org/mock/gomock"
)

// MockStore is a mock of Store interface.
type MockStore struct {
	ctrl     *gomock.Controller
	recorder *MockStoreMockRecorder
	isgomock struct{}
}

// MockStoreMockRecorder is the mock recorder for MockStore.
type MockStoreMockRecorder struct {
	mock *MockStore
}

// NewMockStore creates a new mock instance.
func NewMockStore(ctrl *gomock.Controller) *MockStore {
	mock := &MockStore{ctrl: ctrl}
	mock.recorder = &MockStoreMockRecorder{mock}
	return mock
}

// EXPECT returns an object that allows the caller to indicate expected use.
func (m *MockStore) EXPECT() *MockStoreMockRecorder {
	return m.recorder
}

// Delete mocks base method.
func (m *MockStore) Delete(ctx context.Context, id int) error {
	m.ctrl.T.Helper()
	ret := m.ctrl.Call(m, "Delete", ctx, id)
	ret0, _ := ret[0].(error)
	return ret0
}

// Delete indicates an expected call of Delete.
func (mr *MockStoreMockRecorder) Delete(ctx, id any) *gomock.Call {
	mr.mock.ctrl.T.Helper()
	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Delete", reflect.TypeOf((*MockStore)(nil).Delete), ctx, id)
}

// Get mocks base method.
func (m *MockStore) Get(ctx context.Context, id int) (User, error) {
	m.ctrl.T.Helper()
	ret := m.ctrl.Call(m, "Get", ctx, id)
	ret0, _ := ret[0].(User)
	ret1, _ := ret[1].(error)
	return ret0, ret1
}

// Get indicates an expected call of Get.
func (mr *MockStoreMockRecorder) Get(ctx, id any) *gomock.Call {
	mr.mock.ctrl.T.Helper()
	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Get", reflect.TypeOf((*MockStore)(nil).Get), ctx, id)
}

// Save mocks base method.
func (m *MockStore) Save(ctx context.Context, u User) error {
	m.ctrl.T.Helper()
	ret := m.ctrl.Call(m, "Save", ctx, u)
	ret0, _ := ret[0].(error)
	return ret0
}

// Save indicates an expected call of Save.
func (mr *MockStoreMockRecorder) Save(ctx, u any) *gomock.Call {
	mr.mock.ctrl.T.Helper()
	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Save", reflect.TypeOf((*MockStore)(nil).Save), ctx, u)
}

go test -count=1 -v -run 'TestUpgrade' . 2>&1 | grep -vE '^(=== RUN|PASS|ok)' | sed -E 's/ \([0-9.]+s\)//'
echo "--- violated expectations ---"
DEMO=1 go test -count=1 -run 'TestDemo' . 2>&1 | sed -E 's/\([0-9.]+s\)//; s#/[^ ]*/##; /^FAIL/d; /^exit status/d' | head -30

--- PASS: TestUpgrade
    --- PASS: TestUpgrade/saves_the_pro_plan_once
    --- PASS: TestUpgrade/already_pro_never_saves
    --- PASS: TestUpgrade/not_found_is_wrapped
    --- PASS: TestUpgrade/matcher_and_DoAndReturn
--- violated expectations ---
--- FAIL: TestDemoMissingSave 
    controller.go:97: missing call(s) to *main.MockStore.Get(is anything, is equal to 7 (int)) users_test.go:69
    controller.go:97: missing call(s) to *main.MockStore.Save(is anything, is equal to {7  pro} (main.User)) users_test.go:70
    controller.go:97: aborting test due to missing call(s)
--- FAIL: TestDemoUnexpectedCall 
    users.go:37: Unexpected call to *main.MockStore.Save([context.Background {7  pro}]) at users.go:37 because: there are no expected calls of the method "Save" for that receiver

packages:
  example.com/app:
    interfaces:
      Store:

// from mockery's documentation; not run in this article
store := NewMockStore(t)
store.EXPECT().Get(mock.Anything, 7).Return(User{ID: 7, Plan: "free"}, nil)