我可以使用嵌套接口模拟出库代码吗？ [重复]

Question

This question already has an answer here:

• How can I mock multiple types when the signature of a concrete method refers to another concrete type, not its interface? 1 answer

I am trying to mock a 3rd party library in a test in my go code. But I cannot compile the approach that I have taken. Is there any way to make this work, or another approach I can take if I want to mock the result of T2.M2?

package main

import (
    "fmt"
)

// Two types in a library that I dont have control over
type T1 struct {}
func (T1) M1() T2 {
    return T2{}
}
type T2 struct {}
func (T2) M2() {
    fmt.Println("hello world")
}

// I created these interfaces in order to assign an instance of T1 
// to a variable of type I1 so that I can mock the behavior of T2.M2()
// problem is that this doesn't compile.
type I1 interface {
    M1() I2
}
type I2 interface {
    M2() // I want to mock this method
}

// Then I would be able to create a mock
type Mock1 struct {}
func (Mock1) M1() I2 {
    return Mock2{}
}
type Mock2 struct {}
func (Mock2) M2() {
    fmt.Println("HELLO WORLD")
}

func main() {
    var i1 I1
    i1 = T1{}
    i1.M1().M2()
    i1 = Mock1{}
    i1.M1().M2()
}

https://play.golang.org/p/sv-Uuuke1dr

</div>

Answer 1

Wrap your dependency in structs embedding dependent types:

// answer wrap your dependency
type Ta1 struct {
  T1
}
func (Ta1) M1() I2 {
    return Ta2{}
}
type Ta2 struct {
   T2
}

Then it will work:

func main() {
    var i1 I1
    i1 = Ta1{}
    i1.M1().M2()
    i1 = Mock1{}
    i1.M1().M2()
}

Try on https://play.golang.org/p/aHr78dY_c9a