fix(mocks): $timeout.flushNext should throw if nothing to flush

Author: IgorMinar

src/ngMock/angular-mocks.js

@@ -131,6 +131,10 @@ angular.mock.$Browser = function() {
   self.defer.flushNext = function(expectedDelay) {
     var tick = self.deferredFns.shift();
 
+    if (!tick) {
+      throw new Error("Nothing to be flushed!");
+    }
+
     if (angular.isDefined(expectedDelay) && (tick.time !== expectedDelay)) {
       throw new Error("Expected a task to be scheduled with " + expectedDelay + "ms delay, but it was " + tick.time +
                       "ms.");

test/ngMock/angular-mocksSpec.js

@@ -440,6 +440,13 @@ describe('ngMock', function() {
         $timeout.flushNext(4000);
       }).toThrow("Expected a task to be scheduled with 4000ms delay, but it was 100ms.");
     }));
+
+
+    it("should throw an exception when no task was scheduled but flushNext() was called", inject(function($timeout) {
+      expect(function() {
+        $timeout.flushNext();
+      }).toThrow("Nothing to be flushed!");
+    }));
   });