public void TestCounterSubject()
{
Counter counter = new Counter();
MockObserver observer1 = new MockObserver();
MockObserver observer2 = new MockObserver();
counter.RegisterObserver(observer1);
counter.RegisterObserver(observer2);
counter.Increment();
Assert.IsTrue(observer1.GetCount() == 1);
Assert.IsTrue(observer2.GetCount() == 1);
counter.UnregisterObserver(observer1);
counter.Increment();
Assert.IsTrue(observer1.GetCount() == 1);
Assert.IsTrue(observer2.GetCount() == 2);
}
