Robolectric test fails while it should succeed

I am making an Android application that uses Retrofit as a Rest client and Robolectric for testing. I am new to Android testing and I am stuck on something for a while now. I have a login activity with 2 edittext, a button and a label (TextView for possible errors). All of my tests are working perfectly, but when I test things that happen after the callback then Robolectric doesn't see that somehow..

Example of a test that succeed (before callback):

@Test
@Config(qualifiers = "values")
public void emptyPasswordShouldShowError() throws Exception
{
    txtUsername.setText("testuser1@kdg.be");
    btnLogin.performClick();
    ANDROID.assertThat(txtPassword).hasError("The password is empty");
}

(Oh and I am also using Fest for testing: http://ift.tt/1JzsMko).

Example of a test that fails (after callback):

@Test
@Config(qualifiers = "values")
public void wrongLoginShouldShowError() throws Exception
{
    txtUsername.setText("wronguser@wronguser.be");
    txtPassword.setText("wrongpassword");
    btnLogin.performClick();
    ANDROID.assertThat(lblErrorMessage).hasText("Wrong login!");
}

I've also tested it with toasts and other things but they all fail!

This is the function that goes off when you click on the login-button:

private void loginUser() {
        final String username = txtUsername.getText().toString();
        final String password = txtPassword.getText().toString();
        if(!checkForErrors(username, password)) {
            User user = new User(username, password);
            api.loginUser(user, new Callback<User>() {
                @Override
                public void success(User user, Response response) {
                    SharedPreferences sharedPreferences = getSharedPreferences("session", Context.MODE_PRIVATE);
                    SharedPreferences.Editor editor = sharedPreferences.edit();
                    String sessionId = getCookie(response.getHeaders());
                    editor.putString("sessionId", sessionId);
                    editor.putString("username", username);
                    editor.apply();
                    startDashboardActivity();
                }

                @Override
                public void failure(RetrofitError retrofitError) {
                   lblErrorMessage.setText(getString(R.string.error_wrong_login));
                }
            });
        }
    }

If I test it myself on my Emulator it works perfectly! But when I test it using Robolectric I always get this error: java.lang.AssertionError: Expected text "Wrong login!" but was <>.

Here is a screenshot of my app with the working error

I have no idea why this test fails, I hope you can help me out!

Thanks in advance!