https://github.com/GoogleCloudPlatform/nodejs-docs-samples/pull/16#discussion_r42408072

Author: stephenplusplus

datastore/query.js

@@ -152,18 +152,47 @@ Query.prototype.testKindlessQuery = function(callback) {
 };
 
 Query.prototype.testRunQueryProjection = function(callback) {
+  var self = this;
   var query = this.projectionQuery;
 
-  // jshint unused:false
+  // Overwrite the mock to actually run the query.
+  datastore.runQuery = function(query, queryCallback) {
+    // Restore the mock.
+    datastore.runQuery = function() {};
+
+    self.datastore.runQuery(query, function(err) {
+      if (err) {
+        callback(err);
+        return;
+      }
+
+      queryCallback.apply(null, arguments);
+
+      if (priorities.length === 0 || percentCompletes.length === 0) {
+        callback(new Error('Projection lists did not build up.'));
+      } else {
+        callback();
+      }
+    });
+  };
+
+  // jshint unused:false, camelcase:false
   // [START run_query_projection]
-  datastore.runQuery(query, function(err, entities) {
-    if (!err) {
-      // Entities found.
+  var priorities = [];
+  var percentCompletes = [];
+
+  datastore.runQuery(query, function(err, tasks) {
+    if (err) {
+      // An error occurred while running the query.
+      return;
     }
+
+    tasks.forEach(function(task) {
+      priorities.push(task.data.priority);
+      percentCompletes.push(task.data.percent_complete);
+    });
   });
   // [END run_query_projection]
-
-  this.datastore.runQuery(query, callback);
 };
 
 Query.prototype.testKeysOnlyQuery = function(callback) {