get_customer_test.go

        t.Run("returns an error on failure to get customer booking count", func(t *testing.T) {
                var customerID uint = 1
                var want = errors.New("oh no!")

                ctrl := gomock.NewController(t)

                mockCustomerGetter := NewMockCustomerGetter(ctrl)
                mockCustomerBookingCounter := NewMockCustomerGetter(ctrl)

                mockCustomerGetter.EXPECT().GetCustomer(customerID).Return(entities.Customer{}, nil)
                mockCustomerBookingCounter.EXPECT().CountCustomerBookings(customerID).Return(0, want)

                usecase := usecases.NewGetCustomerUseCase(mockCustomerGetter, mockCustomerBookingCounter)
                if _, got := usecase(customerID); got != want {
                        t.Fatalf("want error: %s, got error: %s", want, got)
                }
        })

        t.Run("returns customer information on success", func(t *testing.T) {
                var (
                        customerID     uint = 1
                        firstName           = "firstname"
                        postCode            = "postcode"
                        numberBookings uint = 10
                )

                ctrl := gomock.NewController(t)

                mockCustomerGetter := NewMockCustomerGetter(ctrl)
                mockCustomerBookingCounter := NewMockCustomerGetter(ctrl)

                mockCustomerGetter.EXPECT().GetCustomer(customerID).Return(entities.Customer{
                        FirstName: firstName,
                        Postcode:  postCode,
                }, nil)
                mockCustomerBookingCounter.EXPECT().CountCustomerBookings(customerID).Return(numberBookings, nil)

                want := entities.Customer{
                        FirstName:      firstName,
                        Postcode:       postCode,
                        NumberBookings: numberBookings,
                }

                usecase := usecases.NewGetCustomerUseCase(mockCustomerGetter, mockCustomerBookingCounter)
                if got := usecase(customerID); got != want {
                        t.Fatalf("got: %#v, want: %#v", got, want)
                }
        })
}