Update README, changelog, remove test

Author: collinjackson

packages/espresso/CHANGELOG.md

@@ -1,3 +1,3 @@
 ## 0.0.1
 
-* TODO: Describe initial release.
+* Initial open-source release of Espresso bindings for Flutter.

packages/espresso/README.md

@@ -2,8 +2,70 @@
 
 A new flutter plugin project.
 
-## Getting Started
+This package provides bindings for Espresso tests of Flutter apps.
 
+## Installation
 
+See the example app for test layout.
 
 Add ```android:usesCleartextTraffic="true"``` to your ```<application>``` in your AndroidManifest.xml.
+
+## Sample usage:
+
+```
+@RunWith(AndroidJUnit4.class)
+public final class SharedPreferencesIntegrationTest {
+
+ @Rule
+ public ActivityTestRule<MainActivity> myActivityTestRule =
+           new ActivityTestRule<>(MainActivity.class, true, false);
+
+ @Before
+ public void setUp() {
+   ActivityScenario.launch(MainActivity.class);
+ }
+
+ @Test
+ public void tapToCheckPersistentData() throws Exception {
+   onFlutterWidget(FlutterMatchers.withTooltip("Clear")).perform(FlutterActions.click());
+   onFlutterWidget(FlutterMatchers.withTooltip("Increment")).perform(FlutterActions.click());
+   onFlutterWidget(FlutterMatchers.withValueKey("ResultText")).check(
+     FlutterAssertions.matches(FlutterMatchers.withText(
+       "Button tapped 1 time.\n\nThis should persist across restarts."
+     )));
+   // kill the app
+   pressBackUnconditionally();
+   // reopen the application
+   myActivityTestRule.launchActivity(null);
+   onFlutterWidget(FlutterMatchers.withValueKey("ResultText")).check(
+      FlutterAssertions.matches(
+      FlutterMatchers.withText(
+      "Button tapped 1 time.\n\nThis should persist across restarts.")));
+   }
+}
+```
+
+The following command line command runs the test locally:
+
+```
+./gradlew app:connectedAndroidTest -Ptarget=`pwd`/../test_driver/shared_preferences.dart
+```
+
+Tests can also be uploaded to Firebase Test Lab:
+
+```
+./gradlew app:assembleAndroidTest
+./gradlew app:assembleDebug -Ptarget=<path_to_test>.dart
+gcloud auth activate-service-account --key-file=<PATH_TO_KEY_FILE>
+gcloud --quiet config set project <PROJECT_NAME>
+gcloud firebase test android run --type instrumentation \
+  --app build/app/outputs/apk/debug/app-debug.apk \
+  --test build/app/outputs/apk/androidTest/debug/app-debug-androidTest.apk\
+  --timeout 2m \
+  --results-bucket=<RESULTS_BUCKET> \
+  --results-dir=<RESULTS_DIRECTORY>
+```
+
+This guarantees that UrlLauncherPlatform.instance cannot be set to an object that `implements`
+UrlLauncherPlatform (it can only be set to an object that `extends` UrlLauncherPlatform).
+