Add support for writing unit tests

.travis.yml

@@ -23,4 +23,4 @@ after_success:
  - chmod +x ./upload_apk.sh
  - ./upload_apk.sh
 
-script: cd android_app && ./gradlew assembleDebug
+script: cd android_app && ./gradlew -i testDebugUnitTest assembleDebug

android_app/app/build.gradle

@@ -31,4 +31,6 @@ dependencies {
     compile "com.android.support:support-v4:${supportLibVersion}"
     compile "com.android.support:appcompat-v7:${supportLibVersion}"
     compile 'com.github.lecho:hellocharts-library:1.5.8@aar'
+
+    testCompile 'junit:junit:4.12'
 }