当依赖项不公开接口时，在GO中模拟依赖项的最佳方法是什么

Question

Im trying to mock https://gopkg.in/olivere/elastic.v2 and its proven to be a nightmare. I usually use gomock but I can't because theres no interface file for the dep. What's the best way to go about this?

Answer 1

Create your own interface.

It doesn't even need to be complete, either, it only needs to cover the methods you actually use.

Suppose you have a type Foo with the following methods: Bar(), Baz(), and Qux().

And you use this in your code:

func Frobnicate(f *Foo) err {
    if err := f.Bar() error; err != nil {
        return err
    }
    return nil
}

Just change this to use your new custom interface:

type barer interface() {
    Bar() error
}

Then update your function signature:

func Frobnicate(f fooer) err {
    // The rest the same as before

Now create your own fooer implementation, and mock away.

If the type you need to mock is a simple struct with data, instead of with methods, you may wrap the method with getter/setter methods, so that an interface will work around it. Example, given this type:

type Foo struct {
    Name string
}

You can create a wrapper:

type FooWrapper struct {
    Foo
}

func (w *FooWrapper) Name() string {
    return w.Foo.Name
}

Now the Foo type can be accessed using a custom interface for mocking.