Golang http handler testing with inner functions - go

Question

I want to build a testing part for my http handlers, and I want to use the http handler functions how they are, but I want to have separate functions that mock the db part of the handling. What I have in mind is something like:
package main
import (
"log"
"testing"
)
// DB functions
type UserDBFunctions interface {
InsertUser() string
}
type UserDB struct {
}
func (u UserDB) InsertUser() string {
return "hello"
}
// http handler functions
type UserHandlerFunctions interface {
Register() string
}
type UserHandler struct {
userDb *UserDB
}
func newUserHandler() UserHandler {
return UserHandler{userDb: new(UserDB)}
}
func (u UserHandler) Register() string {
str := u.userDb.InsertUser()
return str + " world"
}
func main() {
var i UserHandlerFunctions = newUserHandler()
str := i.Register()
log.Println(str)
}
// test functions
type FakeUserDBFunctions interface {
InsertUser() string
}
type FakeUserDB struct {
}
func (u FakeUserDB) InsertUser() string {
return "bye"
}
func newFakeUserHandler() UserHandler {
return UserHandler{userDb: *UserDB(&FakeUserDB{})}
}
func TestRegisterUser(t *testing.T) {
t.Run("register user", func(t *testing.T) {
var i UserHandlerFunctions = newFakeUserHandler()
str := i.Register()
log.Println(str)
})
}
So the first interface is for the real db functions, then there is the http handler which calls the db function and below the main() function there should be the tests with a mockup of the db function. But this part doesn't work. How do I replace the real interface in the newUserHandler by a mockup.
I would really appreciate help. 😊

Answer 1

The UseHandler shall use UserDBFunctions instead of UserDB.
type UserHandler struct {
userDb UserDBFunctions
}
Here is the modified one https://play.golang.org/p/nLiaomKA2NH