Golang，如何用Gock模拟休息

I am new to Go and I am trying to write an unit test to check if the JSON data that I am retrieving from my API is being successfully marshalled into its respective objects.

I am using the go-resty API to make the request and the gock API to try to mock it.

Here is the function that I am trying to test:

func GetTasks() []Task {
    resp, err := MakeRequest().
        SetResult([]Task{}).
        Get("http://my-api/task")

    if err != nil {
        log.Errorf("error when try to get tasks list %s", err)
        return []Task{}
    }

    tasks := resp.Result()
    t, ok := tasks.(*[]Task)
    if ok != true {
        log.Errorf("error when try convert tasks list response %s", ok)
        return []Task{}
    }
    return *t
}

And here is the test code:

func Test_GetTasks(t *testing.T) {
    testData, err := ioutil.ReadFile("../testdata/task-list.json")
    if err != nil {
        t.Error("Error retrieving json test data: %s", err)
        t.Fail()
    }

    defer gock.Off()
    gock.New("http://my-api").
        Get("/task").
        Reply(200).
        JSON(testData)

    var tasks []Task
    tasks = GetTasks()

    t.Logf("Tasks: %d", len(tasks))

    if len(tasks) == 0 {
        t.Error("No tasks were retrieved")
    }
}

What I am doing wrong here?