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')
 }