Concurrency With Gomock
I promise this gonna be quick one (and also helpful)
Okay, so still with Go unit testing and mocking. Have you ever encountered when you want to test a function and that function calls a dependency in other goroutines and makes your test inconsistent?
You do? Okay great let’s solve it!
Okay, to solve this problem, you gonna need:
- Go’s sync.WaitGroup and
- GoMock’s
.Domethod.
Let’s say you have this service
package service
import (
"context"
"fmt"
)
type Repository interface {
DoSomething() error
}
type Service struct {
repository Repository
}
func NewService(r Repository) *Service {
return &Service{repository: r}
}
func (s *Service) DoSomething(ctx context.Context) error {
go func() {
if err := s.repository.DoSomething(); err != nil {
fmt.Println("error happening!!!")
}
}()
return nil
}
to this this part of the function, you gonna need to do something like this…
package service_test
import (
"context"
"example/service"
"example/service/mock"
"fmt"
"sync"
"testing"
"github.com/golang/mock/gomock"
"github.com/stretchr/testify/assert"
)
func TestDoSomething(t *testing.T) {
t.Run("return nil", func(t *testing.T) {
ctrl := gomock.NewController(t)
defer ctrl.Finish()
var wg sync.WaitGroup
ctx := context.Background()
mockRepository := mock.NewMockRepository(ctrl)
// !!! IMPORTANT NOTE !!!
// The function (or anonymous function) that you passed
// into `.Do` method should have exact signature with
// the method that you called in other goroutines.
wg.Add(1)
mockRepository.
EXPECT().
DoSomething().
Times(1).
Return(nil).
Do(func() {
defer wg.Done()
})
service := service.NewService(mockRepository)
actual := service.DoSomething(ctx)
wg.Wait()
assert.NoError(t, actual)
})
t.Run("return an error", func(t *testing.T) {
ctrl := gomock.NewController(t)
defer ctrl.Finish()
var wg sync.WaitGroup
ctx := context.Background()
mockRepository := mock.NewMockRepository(ctrl)
// !!! IMPORTANT NOTE !!!
// The function (or anonymous function) that you passed
// into `.Do` method should have exact signature with
// the method that you called in other goroutines.
wg.Add(1)
mockRepository.
EXPECT().
DoSomething().
Times(1).
Return(fmt.Errorf("shit happened!")).
Do(func() interface{} {
defer wg.Done()
return fmt.Errorf("shit happened!")
})
service := service.NewService(mockRepository)
actual := service.DoSomething(ctx)
wg.Wait()
assert.NoError(t, actual)
})
}
Thank you everyone!
PS: if you want to read more (or understand more) about this, you can go read this good Medium article: Unit Testing and mock calls inside goroutines by Jeffy Mathew