Expected value is changed in Return Method of mockgen during its call

I am new to Go and recently, I am trying to write test cases using gomock package. I encountered a strange problem. I am trying to write test case for GetUsers whose
implementation is

func (ctrl *HttpController) GetUsers(w http.ResponseWriter, r *http.Request) {

	users := ctrl.DS.GetUsers()
	
    // changed the name of the user
	users[0].Name = "User C"
	utility.JsonOkResponse(w, users)
} 

This is my test function

func TestGetUsers_Success(t *testing.T) {

	// setup mock interfaces
	ctrl, ds, _ := setup(t)

	// setup expected function calls
	expected := mock_data.Users
	ds.EXPECT().GetUsers().Return(expected)

	// create the request
	req := httptest.NewRequest("GET", "/users", nil)

	// generate router
	mux := mux.NewRouter()
	mux.HandleFunc("/users", ctrl.GetUsers)

	// create response recorder
	resp := httptest.NewRecorder()
	mux.ServeHTTP(resp, req)

	// check response contents
	assert.Equal(t, http.StatusOK, resp.Code)

	var users []model.User
	json.Unmarshal(resp.Body.Bytes(), &users)

	assert.Equal(t, expected, users)
}

These are the mock_data.Users

var Users = []model.User{user1, user2}

// sample user data
var user1 = model.User{
	ID:       1,
	Name:     "User A",
	Email:    "usera@gmail.com",
}

var user2 = model.User{
	ID:       2,
	Name:     "User B",
	Email:    "userb@gmail.com",
}

Now, I was expermenting with different scenarios for better understanding. So, in this case my test case should fail (although it still passes) because I changed one of the user's name in GetUsers function but strangely, the test case still passes and when I do assert.Equal(t, expected, users) the value in the expected is also changed with new user name User C. Is the expected value passed as pointer in Return method of mockgen or Am I missing something basic ?

This happens because when you do expected := mock_data.Users you are making a copy of the slice header, but not the underlying array, so changes to the array of the first slice will change the other. Please take a look at this article for more details.

If you want to make a copy of the slice you need to use the builtin copy function, like so:

expected := make([]model.User, len(mock_data.Users))
copy(expected, mock_data.Users)