MyActivityTest.java

package com.example.joshskeen.myapplication;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.robolectric.Robolectric;
import org.robolectric.RobolectricGradleTestRunner;
import org.robolectric.annotation.Config;

import static org.assertj.android.api.Assertions.assertThat;


@RunWith(RobolectricGradleTestRunner.class)
@Config(constants = BuildConfig.class, sdk = 21)
public class MyActivityTest {

    private MyActivity mActivity;

    @Before
    public void setup() {
        mActivity = Robolectric.buildActivity(MyActivity.class).create().get();
    }

    @Test
    public void myActivityAppearsAsExpectedInitially() {
        assertThat(mActivity.mClickMeButton).hasText("Click me!");
        assertThat(mActivity.mHelloWorldTextView).hasText("Hello world!");
    }

    @Test
    public void clickingClickMeButtonChangesHelloWorldText() {
        assertThat(mActivity.mHelloWorldTextView).hasText("Hello world!");
        mActivity.mClickMeButton.performClick();
        assertThat(mActivity.mHelloWorldTextView).hasText("HEY WORLD");
    }

}