C#中的单元测试:第二次调用模拟方法时返回另一个var

当尝试对方法进行单元测试时，我遇到了一个问题。该方法的任务是移动树中的节点。该树是通过"预订单树遍历"方法构建的。http://blogs.sitepoint.com/hierarchical-data-database-2/此方法使用节点的"左"answers"右"值将其定位在树中。

在方法中，将更改节点的Lft和Rgt值。在我的测试用例中，我将把节点"Meat"移到"Banana"下。

        var Food = new Node { Id = Guid.NewGuid(), Title = "Food", Ordinal = 0,Depth = 0, Lft = 1, Rgt = 18};
        var Fruit = new Node { Id = Guid.NewGuid(), Title = "Fruit", ParentNode = Food, Depth = 1, Ordinal = 0, Lft = 2, Rgt = 11 };
        var Red = new Node { Id = Guid.NewGuid(), Title = "Red", ParentNode = Fruit, Depth = 2, Ordinal = 0, Lft = 3, Rgt = 6 };
        var Cherry = new Node { Id = Guid.NewGuid(), Title = "Cherry", ParentNode = Red, Depth = 3, Ordinal = 0, Lft = 4, Rgt = 5 };
        var Yellow = new Node { Id = Guid.NewGuid(), Title = "Yellow", ParentNode = Fruit, Depth = 2, Ordinal = 1, Lft = 7, Rgt = 10 };
        var Banana = new Node { Id = Guid.NewGuid(), Title = "Banana", ParentNode = Yellow, Depth = 3, Ordinal = 0, Lft = 8, Rgt = 9 };
        var Meat = new Node { Id = Guid.NewGuid(), Title = "Meat", ParentNode = Food, Depth = 1, Ordinal = 1, Lft = 12, Rgt = 17 };
        var Beef = new Node { Id = Guid.NewGuid(), Title = "Beef", ParentNode = Meat, Depth = 2, Ordinal = 0, Lft = 13, Rgt = 14 };
        var Pork = new Node { Id = Guid.NewGuid(), Title = "Pork", ParentNode = Meat, Depth = 2, Ordinal = 1, Lft = 15, Rgt = 16 };
        var allNodes = new List<Node> {Food, Fruit, Red, Cherry, Yellow, Banana, Meat, Beef, Pork};
        var descendantsOfNodeFood = new List<Node>
                                  {
                                     Beef,
                                     Cherry,
                                     Red,
                                     Yellow,
                                     Pork,
                                     Banana,
                                     Meat,
                                     Fruit
                                  };
        var descendantsOfNodeFruit = new List<Node>
                                  {
                                     Red,
                                     Cherry,
                                     Banana,
                                     Yellow
                                  };
        var descendantsOfNodeRed = new List<Node>
                                  {
                                     Cherry
                                  };
        var descendantsOfNodeCherry = new List<Node> { };
        var descendantsOfNodeYellow = new List<Node>
                                  {
                                     Banana
                                  };
        var descendantsOfNodeBanana = new List<Node> { };
        var descendantsOfNodeMeat = new List<Node>
                                  {
                                     Beef,
                                     Pork
                                  };
        var descendantsOfNodeBeef = new List<Node> { };
        var descendantsOfNodePork = new List<Node> { };
        //Mock the node repository
        _mockNodeRepository.Setup(x => x.LoadNode(Food.Id)).Returns(Food);
        _mockNodeRepository.Setup(x => x.GetDescendants(Food.Id, It.IsAny<bool>())).Returns(descendantsOfNodeFood);
        _mockNodeRepository.Setup(x => x.GetDescendants(Fruit.Id, It.IsAny<bool>())).Returns(descendantsOfNodeFruit);
        _mockNodeRepository.Setup(x => x.GetDescendants(Red.Id, It.IsAny<bool>())).Returns(descendantsOfNodeRed);
        _mockNodeRepository.Setup(x => x.GetDescendants(Cherry.Id, It.IsAny<bool>())).Returns(descendantsOfNodeCherry);
        _mockNodeRepository.Setup(x => x.GetDescendants(Yellow.Id, It.IsAny<bool>())).Returns(descendantsOfNodeYellow);
        _mockNodeRepository.Setup(x => x.GetDescendants(Banana.Id, It.IsAny<bool>())).Returns(descendantsOfNodeBanana);
        _mockNodeRepository.Setup(x => x.GetDescendants(Meat.Id, It.IsAny<bool>())).Returns(descendantsOfNodeMeat);
        _mockNodeRepository.Setup(x => x.GetDescendants(Beef.Id, It.IsAny<bool>())).Returns(descendantsOfNodeBeef);
        _mockNodeRepository.Setup(x => x.GetDescendants(Pork.Id, It.IsAny<bool>())).Returns(descendantsOfNodePork);
        _mockNodeRepository.Setup(x => x.GetNodes()).Returns(allNodes);

运行测试时，除Meat的Lft和Rgt值外，所有值都设置为正确值。（应该是9-10）我将问题追溯到方法"GetDescendants（Meat.Id，It.IsAny（））"的mock。在我尝试测试的方法中，这个方法将被调用两次。第一次它应该返回一个节点为"牛肉"answers"猪肉"的列表。第二次，节点"牛肉"被放在"香蕉"下，它应该返回一个只有节点"猪肉"的列表。

谁能帮我弄清楚mock第一次如何返回一个有2个节点的列表，第二次如何返回只有一个节点的名单？

我使用"Microsoft.VisualStudio.TestTools.UnitTesting；"answers"Moq；"进行单元测试。

returning different values on each invocation
var mock = new Mock<IFoo>();
var calls = 0;
mock.Setup(foo => foo.GetCountThing())
    .Returns(() => calls)
    .Callback(() => calls++);
// returns 0 on first invocation, 1 on the next, and so on
Console.WriteLine(mock.Object.GetCountThing());

var mock = new Mock<IFoo>();
bool firstCall = true;
mock.Setup(foo => foo.GetCountThing())
.Returns(() => firstCall ? list1 : list2)
.Callback(() => firstCall = false);