implement testing and create a simple test for Userlist

core.gradle

@@ -19,6 +19,10 @@ android {
         targetCompatibility JavaVersion.VERSION_1_8
     }
 
+    kotlinOptions {
+        jvmTarget = JavaVersion.VERSION_1_8.toString()
+    }
+
     testOptions {
         unitTests.returnDefaultValues = true
     }