如何将这个api提取到接口，以便可以在测试中模拟它？

Question

So currently I have a http handler that looks like:

type App struct {

}
func (a *App) someHandler(w http.ResponseWriter, r *http.Request) {
        var api = slack.New("TOKEN")
        users = api.GetUsers()
}

I want to create an interface for this slack.New("...") call so that in my tests the api doesn't make network requests to slack.

How can I mock this New call?

The call New("TOKEN") returns a *Client, see the link below:

func New(token string, options ...Option) *Client {
    s := &Client{
        token:      token,
        httpclient: &http.Client{},
        log:        log.New(os.Stderr, "nlopes/slack", log.LstdFlags|log.Lshortfile),
    }

    for _, opt := range options {
        opt(s)
    }

    return s
}

https://github.com/nlopes/slack/blob/0f8db5050731c50359e319cf253af5b9997a2b1e/slack.go#L84

I haven't used interfaces that much so not sure if this can't be put in a interface since the call to New is like a constructor?

Answer 1

You can't mock the slack.New call itself, instead you have to create a mock that behaves like this api object. To do this put the api onto the App struct but as an interface:

type SlackClient interface {
    GetUsers() []string
}

type App struct {
    api SlackClient
}

func (a *App) someHandler(w http.ResponseWriter, r *http.Request) { 
    users = a.api.GetUsers() 
}

You then have to move the call to slack.New into whatever constructs the App (for instance your main function or a NewApp constructor function):

app = App{api: slack.New("TOKEN")}

The *Client this returns has a GetUsers method on it so will match the interface we have defined.

The test then does something similar with a mock:

type mockSlackClient struct {

}

func (m *mockSlackClient) GetUsers() []string {
    return nil
}

func TestSomeHandler(t *testing.T) {
    appToTest := App{api: &mockSlackClient{})

    appToTest.someHandler(httptest.NewRecorder(), nil)
}

Again as the *mockSlackClient has a GetUsers method on it it will satisfy the interface so you will be able to use it on the App.