Abstarct functions implemented in MockExecutors, MockBaseClient and GraphServiceClientTest. Built Successfully.

Author: Nakul Sabharwal

src/test/java/com/microsoft/graph/concurrency/MockExecutors.java

@@ -52,4 +52,9 @@ public <Result> void performOnForeground(final ClientException exception,
                                              final ICallback<Result> callback) {
         callback.failure(exception);
     }
+    
+    @Override
+    public void shutdownBackgroundExecutors(){
+    	
+    }
 }

src/test/java/com/microsoft/graph/core/MockBaseClient.java

@@ -78,5 +78,9 @@ public void setHttpProvider(final IHttpProvider httpProvider) {
     public void setSerializer(final ISerializer serializer) {
         mSerializer = serializer;
     }
+    
+    public void shutdown() {
+    	
+    }
 
 }

src/test/java/com/microsoft/graph/requests/extensions/GraphServiceClientTest.java

@@ -111,6 +111,11 @@ public <Result> void performOnForeground(ClientException exception,
                     ICallback<Result> callback) {
                 // do nothing
             }
+            
+            @Override
+            public void shutdownBackgroundExecutors() {
+            	
+            }
 
         };
         IGraphServiceClient client = GraphServiceClient.builder() //