Conditional Mocking in Go

I want to mock Rest API calls in GoLang based on certain condition.
For example, i have a method defined like below :

func Method() {
  resp1, err := DoSomething1()
  resp2, err := DoSomething2()
}

func DoSomething1() (*http.Response, error) {
  return Get(url string)
}

func DoSomething2() (*http.Response, error) {
  return Get(url string)
}

Now, i want to define my mock response for each get calls separately. i.e when i call DoSomething1() from Method(), i want to mock the get call and return response R1 and when i call DoSomething2() from Method(), i want to mock the get call and return response R2.

So far, i have been able to mock a single get call that would return same response for any request by defining Get as an interface and mocking it, however i am trying to define responses for each of these calls.

Below is the mock interface that i have defined that i am using to mock get/post calls :

package clientMock

import (
	"net/http"
)

type MockClient struct {
}

var (
	GetMock  func(url string, queryParams map[string]interface{}, headerParams map[string]interface{}) (*http.Response, error)
	PostMock func(url string, reqBody interface{}, queryParams map[string]interface{}, headerParams map[string]interface{}) (*http.Response, error)
)

func (m MockClient) Get(url string, queryParams map[string]interface{}, headerParams map[string]interface{}) (*http.Response, error) {
	return GetMock(url, queryParams, headerParams)
}

func (m MockClient) Post(url string, reqBody interface{}, queryParams map[string]interface{}, headerParams map[string]interface{}) (*http.Response, error) {
	return PostMock(url, reqBody, queryParams, headerParams)
}

Below is the sample Test Class that i have defined for testing Method, however unable to figure out how can i change the mock response when DoSomething2() is being called from Method() :

func TestHandleSuccess(t *testing.T) {

	resBody := `{"instance_url":"instance_url","access_token":"access_token"}`
	r := ioutil.NopCloser(bytes.NewReader([]byte(resBody)))
	clientMock.GetMock = func(url string, queryParams, headerParams map[string]interface{}) (*http.Response, error) {
		return &http.Response{
			StatusCode: 200,
			Body:       r,
		}, nil

	}

	err := method.Method()
	assert.Nil(t, err)
}

Given the code you've provided, I'm guessing the parameter url passed into Get from your "do something" functions is different (otherwise I'm not sure why you'd need the behavior to change). If this is the case, you could add a condition in your mock to change behavior based on the url.

clientMock.GetMock = func(url string, queryParams, headerParams map[string]interface{}) (*http.Response, error) {
	var resBody string
	if url == "/call1" {
		resBody = `{"instance_url":"instance_url","access_token":"access_token"}`
	} else if url == "/call2" {
		resBody = `{"something":"else"}`
	}
	return &http.Response{
		StatusCode: 200,
		Body:       ioutil.NopCloser(bytes.NewReader([]byte(resBody))),
	}, nil
}

This is how you should think about your code - behavior shouldn't change based on where a call is coming from. Instead, it should change based on the inputs to the function being called. This decouples your function from its caller and makes reuse and refactoring easier.