MainActivityTest.java

package com.jxw.graphql;


import android.support.test.InstrumentationRegistry;
import android.support.test.espresso.IdlingRegistry;
import android.support.test.espresso.idling.CountingIdlingResource;
import android.support.test.runner.AndroidJUnit4;
import android.support.test.rule.ActivityTestRule;

import com.jxw.graphql.test_utils.TestDemoApplication;
import com.jxw.graphql.utils.EspressoIdlingResource;
import com.jxw.graphql.view.MainActivity;

import static android.support.test.espresso.Espresso.onView;
import static android.support.test.espresso.assertion.ViewAssertions.matches;
import static android.support.test.espresso.matcher.ViewMatchers.isDisplayed;
import static android.support.test.espresso.matcher.ViewMatchers.withId;
import static android.support.test.espresso.matcher.ViewMatchers.withText;
import static org.hamcrest.CoreMatchers.not;

import org.junit.After;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.runner.RunWith;


import java.io.IOException;

import okhttp3.mockwebserver.MockResponse;
import okhttp3.mockwebserver.MockWebServer;

@RunWith(AndroidJUnit4.class)
public class TutorialVersionMainActivityTest {
    private CountingIdlingResource countingIdlingResource = EspressoIdlingResource.getCountIdlingResource();

    /**
     * TODO: Move the data containing variables into a data class
     */
    private static final String SUCCESS_RESPONSE = "{" +
            "\"data\":{" +
            "   \"allTeachers\":[" +
            "       {" +
            "           \"name\":\"John Doe\"," +
            "           \"subject\":\"cs300\"," +
            "           \"__typename\":\"Teacher\"," +
            "           \"id\":\"cjs1ucrri6yqe016794qlaclq\"," +
            "           \"createdAt\":\"2019-02-12T14:07:53.000Z\"" +
            "       }," +
            "       {" +
            "           \"name\":\"William Smith\"," +
            "           \"subject\":\"SLT101\"," +
            "           \"__typename\":\"Teacher\"," +
            "           \"id\":\"cjs1uixtu1f6g019507d0ksrk\"," +
            "           \"createdAt\":\"2019-02-12T14:12:41.000Z\"" +
            "       }" +
            "   ]" +
            "}}";
    @Rule
    public ActivityTestRule<MainActivity> mainActivityTestRule = new ActivityTestRule<>(MainActivity.class, true, false);


    @Before
    public void setUp() {
        // Espresso Idling Resource registration
        IdlingRegistry.getInstance().register(countingIdlingResource);
    }

    @Test
    public void testTeachersAreDisplayed() throws IOException {
        /**
         * Setting up mockWebServer at localhost:9900.
         */
        MockWebServer server = new MockWebServer();
        // start the server at port 9900
        server.start(9900);

        /**
         * Get the target application context during testing and cast onto the TestDemoApplication
         */
        TestDemoApplication testApp = (TestDemoApplication) InstrumentationRegistry.getTargetContext().getApplicationContext();
        // Set the base url of the test app using the url of the mocked local server
        testApp.setBaseUrl(server.url("/").toString());

        // Enqueue the response you want the server to respond with when querried in the course to this test.
        server.enqueue(new MockResponse().setBody(SUCCESS_RESPONSE));


        // LAUNCH ACTIVITY
        mainActivityTestRule.launchActivity(null);
        // UI testing 
        onView(withText("John Doe")).check(matches(isDisplayed()));
        onView(withText("William Smith")).check(matches(isDisplayed()));
      
        // Shut down the server when done with testing
        server.shutdown();
    }

    @After
    public void tearDown() {
        IdlingRegistry.getInstance().unregister(countingIdlingResource);
    }
}