开始-如何模拟需要回调的依赖项？

Question

Suppose I have a dependency that looks like this:

type Dependency interface {
    Retrieve(transform func(row *Row) string) []string
}

And I'm using it in code that I'd like to unit test

// ...
result := dep.Retrieve(func(row *Row) string {
    // ... do stuff
})
// ...

This is a contrived example, but consider it for something like gcloud pubsub, which has a Receive method that calls a user-defined function for each message it pulls.

If I use mockgen to get a mock of Dependency, how do I tell the mock how to behave? I'd want it to call its input function some number of times with some sets of input.

Answer 1

Here is some code while trying to understand what you wanted to achieve. I don't use mockgen, but manually, you can do what you want. I totally changed the behavior between the original and the mocked call. Does it answer your questions?

package main

import (
    "fmt"
)

var str = [...]string{
    "world",
    "night",
}

type Dependency interface {
    Get(val string) string
}

type dependency struct {
    i int
}

func (d *dependency) Get(fn func(int) string) string {
    d.i++
    d.i = d.i % len(str)

    return "hello " + fn(d.i)
}

func main() {
    d := dependency{}
    myfn := func(idx int) string { return str[idx] }
    fmt.Println(d.Get(myfn))
    fmt.Println(d.Get(myfn))
    fmt.Println(d.Get(myfn))

    m := mock{}
    fmt.Println(m.Get(myfn))
}

type mock struct {
}

func (m *mock) Get(fn func(int) string) string {
    i := 0
    j := (i + 1) % len(str)
    k := (j + 1) % len(str)

    return "mocked " + fn(i) + fn(j) + fn(k)
}

The play link: https://play.golang.org/p/bb7WrmlIEN