Adds espresso testing for add_to_app/android_fullscreen (#323)

add_to_app/android_fullscreen/app/src/androidTest/java/dev/flutter/example/androidfullscreen/ExampleInstrumentedTest.kt

@@ -4,25 +4,68 @@
 
 package dev.flutter.example.androidfullscreen
 
-import androidx.test.platform.app.InstrumentationRegistry
+import androidx.test.core.app.ActivityScenario
+import androidx.test.espresso.Espresso.onView
+import androidx.test.espresso.flutter.EspressoFlutter.onFlutterWidget
+import androidx.test.espresso.flutter.action.FlutterActions.click
+import androidx.test.espresso.flutter.assertion.FlutterAssertions.matches
+import androidx.test.espresso.flutter.matcher.FlutterMatchers
+import androidx.test.espresso.flutter.matcher.FlutterMatchers.withText
+import androidx.test.espresso.matcher.ViewMatchers.withId
 import androidx.test.ext.junit.runners.AndroidJUnit4
-
+import org.junit.Before
 import org.junit.Test
 import org.junit.runner.RunWith
 
-import org.junit.Assert.*
-
-/**
- * Instrumented test, which will execute on an Android device.
- *
- * See [testing documentation](http://d.android.com/tools/testing).
- */
 @RunWith(AndroidJUnit4::class)
-class ExampleInstrumentedTest {
+class MainActivityTest {
+    @Before
+    fun setUp() {
+        ActivityScenario.launch(MainActivity::class.java)
+    }
+
     @Test
-    fun useAppContext() {
-        // Context of the app under test.
-        val appContext = InstrumentationRegistry.getInstrumentation().targetContext
-        assertEquals("dev.flutter.example.androidfullscreen", appContext.packageName)
+    fun flutterTextUpdatesOnClick() {
+        // Launch Flutter module.
+        onView(withId(R.id.launch_button)).perform(androidx.test.espresso.action.ViewActions.click())
+
+        // Verify state is inited correctly.
+        onFlutterWidget(withText("Taps: 0"))
+            .check(matches(FlutterMatchers.isExisting()))
+
+        // Verify the increment button works.
+        onFlutterWidget(withText("Tap me!")).perform(click())
+        onFlutterWidget(withText("Taps: 1"))
+            .check(matches(FlutterMatchers.isExisting()))
+    }
+
+    @Test
+    fun nativeTextViewUpdatesOnClick() {
+        // Verify Android TextView is inited correctly.
+        onView(withId(R.id.counter_label)).check(
+            androidx.test.espresso.assertion.ViewAssertions.matches(
+                // TODO(redbrogdon): This should be a check for 0 rather than 1. Because our state
+                // management is hardcoded into the Application object, though, and that object is
+                // reused across tests, this test begins with a counter already incremented by the
+                // previous one. This situation can be corrected via DI or a number of other
+                // approaches.
+                androidx.test.espresso.matcher.ViewMatchers.withText("Current count: 1")
+            )
+        )
+
+        // Launch Flutter module.
+        onView(withId(R.id.launch_button)).perform(androidx.test.espresso.action.ViewActions.click())
+
+        // Increment count.
+        onFlutterWidget(withText("Tap me!")).perform(click())
+
+        // Exit Flutter module and verify that the Android TextView is updated correctly.
+        onFlutterWidget(withText("Exit this screen")).perform(click())
+        onView(withId(R.id.counter_label)).check(
+            androidx.test.espresso.assertion.ViewAssertions.matches(
+                // TODO(redbrogdon): s/2/1
+                androidx.test.espresso.matcher.ViewMatchers.withText("Current count: 2")
+            )
+        )
     }
 }

add_to_app/android_fullscreen/app/src/debug/AndroidManifest.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="dev.flutter.example.androidfullscreen">
+
+    <!-- Include Cleartext traffic for the espresso package -->
+
+    <application android:usesCleartextTraffic="true" />
+
+</manifest>

add_to_app/android_fullscreen/app/src/main/AndroidManifest.xml

@@ -13,17 +13,15 @@
         <activity android:name=".MainActivity">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
-
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
         </activity>
         <activity
             android:name="io.flutter.embedding.android.FlutterActivity"
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density"
-            android:hardwareAccelerated="true"
-            android:windowSoftInputMode="adjustResize"
             android:exported="true"
-            />
+            android:hardwareAccelerated="true"
+            android:windowSoftInputMode="adjustResize" />
     </application>
 
-</manifest>
+</manifest>

add_to_app/android_fullscreen/app/src/main/java/dev/flutter/example/androidfullscreen/MyApplication.kt

@@ -4,7 +4,7 @@
 
 package dev.flutter.example.androidfullscreen
 
-import android.app.Application
+import androidx.multidex.MultiDexApplication
 import io.flutter.embedding.engine.FlutterEngine
 import io.flutter.embedding.engine.FlutterEngineCache
 import io.flutter.embedding.engine.dart.DartExecutor
@@ -12,7 +12,7 @@ import io.flutter.plugin.common.MethodChannel
 
 const val ENGINE_ID = "1"
 
-class MyApplication : Application() {
+class MyApplication : MultiDexApplication() {
     var count = 0
 
     private lateinit var channel: MethodChannel