Set up unit test support in Gradle

Summary:
This works now:

```
./gradlew :android:testDebugUnitTest
BUILD SUCCESSFUL in 1s
39 actionable tasks: 39 up-to-date
```

Reviewed By: danielbuechele

Differential Revision: D10101985

fbshipit-source-id: e3d1f17b29652061498d50a9218a94aaebee67e2

android/build.gradle

@@ -26,6 +26,15 @@ android {
         abortOnError false
     }
 
+    sourceSets {
+        test {
+            java {
+                exclude 'com/facebook/sonar/plugins/facebook/**'
+            }
+        }
+    }
+
+
     externalNativeBuild {
         cmake {
             path './CMakeLists.txt'
@@ -45,6 +54,11 @@ android {
         implementation deps.lithoWidget
         implementation deps.rhino
         implementation deps.leakcanary
+
+        testImplementation deps.mockito
+        testImplementation deps.robolectric
+        testImplementation deps.hamcrest
+        testImplementation deps.junit
     }
 }
 

build.gradle

@@ -68,8 +68,10 @@ ext.deps = [
         lithoTesting       : "com.facebook.litho:litho-testing:$LITHO_VERSION",
         // Debugging and testing
         guava              : 'com.google.guava:guava:20.0',
-        robolectric        : 'org.robolectric:robolectric:3.0',
+        robolectric        : 'org.robolectric:robolectric:3.3',
         junit              : 'junit:junit:4.12',
+        hamcrest           : 'org.hamcrest:hamcrest-library:1.3',
+        mockito            : 'org.mockito:mockito-core:1.9.5',
         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',