Add test code

Author: TonyTangAndroid

tester/build.gradle

@@ -1,5 +1,4 @@
 apply plugin: 'java-library'
-
 dependencies {
     api 'junit:junit:4.12'
     api 'commons-io:commons-io:2.6'
@@ -8,6 +7,10 @@ dependencies {
     api 'org.mockito:mockito-core:2.23.4'
     api 'pl.pragmatists:JUnitParams:1.1.1'
     api 'com.squareup.okhttp3:mockwebserver:3.12.1'
+    api "org.assertj:assertj-core:3.11.1"
+    api "org.robolectric:robolectric:3.8"
+    api "com.squareup.okhttp3:mockwebserver:3.12.1"
+    api "com.google.firebase:firebase-admin:6.4.0"
 }
 
 sourceCompatibility = "8"