public void SystemsExecutesIExecuteSystemSystem()
        {
            var system = new UpdateSystemSpy();

            _systems.Add(system);
            _systems.Update();

            Assert.AreEqual(1, system.DidExecute);
        }
        public void ExecutesExecuteSystemSpy()
        {
            var system = new UpdateSystemSpy();

            Assert.AreEqual(0, system.DidExecute);

            system.Update();

            Assert.AreEqual(1, system.DidExecute);
        }