Prevent mock clock timing fns from being spied on

Fixes #826

spec/core/ClockSpec.js

@@ -408,6 +408,41 @@ describe('Clock', function() {
     expect(delayedFunctionScheduler.scheduleFunction).not.toHaveBeenCalled();
   });
 
+  it('identifies its timing functions', function() {
+    const fakeSetTimeout = jasmine.createSpy('global setTimeout');
+    const fakeGlobal = { setTimeout: fakeSetTimeout };
+    const delayedFunctionScheduler = jasmine.createSpyObj(
+      'delayedFunctionScheduler',
+      ['scheduleFunction']
+    );
+    const mockDate = {
+      install: function() {},
+      tick: function() {},
+      uninstall: function() {}
+    };
+    const clock = new jasmineUnderTest.Clock(
+      fakeGlobal,
+      function() {
+        return delayedFunctionScheduler;
+      },
+      mockDate
+    );
+    clock.install();
+
+    expect(
+      fakeGlobal.setTimeout[jasmineUnderTest.Clock.IsMockClockTimingFn]
+    ).toEqual(true);
+    expect(
+      fakeGlobal.clearTimeout[jasmineUnderTest.Clock.IsMockClockTimingFn]
+    ).toEqual(true);
+    expect(
+      fakeGlobal.setInterval[jasmineUnderTest.Clock.IsMockClockTimingFn]
+    ).toEqual(true);
+    expect(
+      fakeGlobal.clearInterval[jasmineUnderTest.Clock.IsMockClockTimingFn]
+    ).toEqual(true);
+  });
+
   describe('setTimeout', function() {
     it('schedules the delayed function with the fake timer', function() {
       const fakeSetTimeout = jasmine.createSpy('setTimeout'),

spec/core/SpyRegistrySpec.js

@@ -135,6 +135,18 @@ describe('SpyRegistry', function() {
       target.spiedFunc();
       expect(originalFunctionWasCalled).toBe(false);
     });
+
+    it('throws if the method is a mock clock method', function() {
+      const spyRegistry = new jasmineUnderTest.SpyRegistry({
+        createSpy: createSpy
+      });
+      const target = { spiedFunc: function() {} };
+      target.spiedFunc[jasmineUnderTest.Clock.IsMockClockTimingFn] = true;
+
+      expect(function() {
+        spyRegistry.spyOn(target, 'spiedFunc');
+      }).toThrowError("Mock clock timing functions can't be spied on");
+    });
   });
 
   describe('#spyOnProperty', function() {