Add integration test

Author: chkuang-g

source/AndroidResolver/test/src/AndroidResolverIntegrationTests.cs

@@ -484,10 +484,24 @@ private static void ValidateAndroidTargetSelected(
                 });
             IntegrationTester.Runner.LogSummaryAndExit();
         }
+
+        // Verify if PlayServicesResolver properties are working properly.
+        var testCaseResult = new IntegrationTester.TestCaseResult(testCase);
+
+        if (String.IsNullOrEmpty(PlayServicesResolver.AndroidGradlePluginVersion)) {
+            testCaseResult.ErrorMessages.Add(String.Format(
+                "PlayServicesResolver.AndroidGradlePluginVersion is empty or null"));
+        }
+
+        if (String.IsNullOrEmpty(PlayServicesResolver.GradleVersion)) {
+            testCaseResult.ErrorMessages.Add(String.Format(
+                "PlayServicesResolver.GradleVersion is empty or null"));
+        }
+
         // Also, set the internal Gradle version to a deterministic version number.  This controls
         // how gradle template snippets are generated by GradleTemplateResolver.
         PlayServicesResolver.GradleVersion = "2.14";
-        testCaseComplete(new IntegrationTester.TestCaseResult(testCase));
+        testCaseComplete(testCaseResult);
     }
 
     /// <summary>