Mock asserting into callbacks - unit-testing

Question

I'm having the following problem when unit testing (working code here]
Assuming we have this:
var (
userDomain UserInterface
Tx TxInterface
)
type UserInterface interface {
Get() (*User, error)
}
type TxInterface interface {
Exec(fn func() error) error
}
type User struct {
ID int64
}
func (u *User) Get() (*User, error) {
return &User{
ID: 1,
}, nil
}
type WithTx struct{}
func (t *WithTx) Exec(fn func() error) error {
/* more logic here */
return fn()
}
Assuming we have the following 2 services:
func GetByID() (*User, error) {
user, err := userDomain.Get()
return user, err
}
func GetByIDWithTx() (*User, error) {
u := &User{}
/** Notice this implementation **/
if err := Tx.Exec(func() error {
user, _ := userDomain.Get()
u = user
return nil
}); err != nil {
log.Print("Tx err", err)
}
return u, nil
}
They are the same but once goes directly to the Get method, the other one runs into a callback fn. So far so go, both works like a charm. Again code is here
I'm trying to mock the userDomain and Tx for unit tests, so my mocks look like this:
var (
getUserFromMock func() (*User, error)
getFromMock func() error
)
type userMock struct{}
func (u *userMock) Get() (*User, error) {
return getUserFromMock()
}
type txMock struct{}
func (t *txMock) Exec(fn func() error) error {
return getFromMock()
}
When testing GetByID I have no problem whatsoever.
func TestGetByID(t *testing.T) {
userDomain = &userMock{}
Tx = &txMock{}
getUserFromMock = func() (*User, error) {
return &User{ID: 3}, nil
}
user, err := GetByID()
if user.ID != 3 {
t.Fatalf("error")
}
if err != nil {
t.Fatalf("error")
}
}
However, When I try to testing GetByIDWithTx, I cannot assert the mock values:
func TestGetByIDWithTx(t *testing.T) {
userDomain = &userMock{}
Tx = &txMock{}
getUserFromMock = func() (*User, error) {
return &User{ID: 4}, nil
}
/**** Mocking callback response ****/
getFromMock = func() error {
return nil
}
user, err := GetByIDWithTx()
if user.ID != 4 {
t.Fatalf("error") /** It fails here **/
}
if err != nil {
t.Fatalf("error")
}
}
I assume, at the moment I'm trying to assert the callback is still running in another routine but I'm just speculating, I don't have any idea what is going on here. I rather not use any library for a spy, I just want to understand how to solve this. Thoughts?
Go PlayGround HERE

Answer 1

You are never calling the fn given to the txmock. Change txMock.Exec to:
type txMock struct{}
func (t *txMock) Exec(fn func() error) error {
return fn()
// return getFromMock()
}
and remove getFromMock() function completely. It will then call getUserFromMock function to get the mocked user.