test($mdUtil): add tests for throttle()

Follow-up on angular#977.

src/core/util/util.spec.js

@@ -23,4 +23,58 @@ describe('util', function() {
     $rootScope.$broadcast('event');
     expect(spy).toHaveBeenCalled();
   }));
+
+  describe('throttle', function() {
+    var delay = 500;
+    var nowMockValue;
+    var originalFn;
+    var throttledFn;
+
+    beforeEach(inject(function($mdUtil) {
+      $mdUtil.now = function () { return nowMockValue; };
+      originalFn = jasmine.createSpy('originalFn');
+      throttledFn = $mdUtil.throttle(originalFn, delay);
+      nowMockValue = 1;    // Not 0, to prevent `!recent` in `throttle()` to evaluate to true
+                           // even after `recent` has been set
+    }));
+
+    it('should immediately invoke the function on first call', function() {
+      expect(originalFn).not.toHaveBeenCalled();
+      throttledFn();
+      expect(originalFn).toHaveBeenCalled();
+    });
+
+    it('should not invoke the function again before (delay + 1) milliseconds', function() {
+      throttledFn();
+      expect(originalFn.callCount).toBe(1);
+
+      throttledFn();
+      expect(originalFn.callCount).toBe(1);
+
+      nowMockValue += delay;
+      throttledFn();
+      expect(originalFn.callCount).toBe(1);
+
+      nowMockValue += 1;
+      throttledFn();
+      expect(originalFn.callCount).toBe(2);
+    });
+
+    it('should pass the context to the original function', inject(function($mdUtil) {
+      var obj = {
+        called: false,
+        fn: function() { this.called = true; }
+      };
+      var throttled = $mdUtil.throttle(obj.fn, delay);
+
+      expect(obj.called).toBeFalsy();
+      throttled.call(obj);
+      expect(obj.called).toBeTruthy();
+    }));
+
+    it('should pass the arguments to the original function', function() {
+      throttledFn(1, 2, 3, 'test');
+      expect(originalFn).toHaveBeenCalledWith(1, 2, 3, 'test');
+    });
+  });
 });