Add basic integration test

Summary:
Just a quick startup test that can save you the time of manually
opening the app.

I don't have any plans of hooking this up in Circle, but it's
still kinda useful to have.

Reviewed By: jknoxville

Differential Revision: D12901590

fbshipit-source-id: a16a1814574d9f27770dcf98c6b238517c589930

android/sample/build.gradle

@@ -5,7 +5,7 @@ android {
     buildToolsVersion rootProject.buildToolsVersion
     defaultConfig {
         minSdkVersion rootProject.minSdkVersion
-        testInstrumentationRunner 'android.support.test.runner.AndroidJUnitRunner'
+        testInstrumentationRunner 'androidx.test.runner.AndroidJUnitRunner'
         applicationId 'com.facebook.flipper.sample'
     }
 
@@ -34,5 +34,9 @@ dependencies {
     implementation deps.soloader
     implementation deps.okhttp3
 
+    // Integration test
+    androidTestImplementation deps.testCore
+    androidTestImplementation deps.testRules
+
     implementation project(':android')
 }

android/sample/src/androidTest/java/com/facebook/flipper/sample/MainActivityTest.java

@@ -0,0 +1,31 @@
+/*
+ *  Copyright (c) 2018-present, Facebook, Inc.
+ *
+ *  This source code is licensed under the MIT license found in the LICENSE
+ *  file in the root directory of this source tree.
+ *
+ */
+package com.facebook.flipper.sample;
+
+import androidx.test.filters.LargeTest;
+import androidx.test.rule.ActivityTestRule;
+import androidx.test.runner.AndroidJUnit4;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+@LargeTest
+@RunWith(AndroidJUnit4.class)
+public class MainActivityTest {
+
+  @Rule
+  public final ActivityTestRule<MainActivity> mTestRule =
+      new ActivityTestRule<>(MainActivity.class);
+
+  @Test
+  public void activityStarts() {
+    final MainActivity activity = mTestRule.getActivity();
+
+    assert activity != null;
+  }
+}

build.gradle

@@ -75,6 +75,8 @@ ext.deps = [
         stetho             : 'com.facebook.stetho:stetho:1.5.0',
         okhttp3            : 'com.squareup.okhttp3:okhttp:3.10.0',
         leakcanary         : 'com.squareup.leakcanary:leakcanary-android:1.6.1',
+        testCore        : 'androidx.test:core:1.0.0',
+        testRules       : 'androidx.test:rules:1.1.0',
         // Plugin dependencies
         rhino              : 'org.mozilla:rhino:1.7.10',
 ]