如何让NUnit测试在SaveOrderAllocation计算逻辑变更时自动失败？

问题背景 #

Presenter层的SaveOrderAllocation方法原本逻辑为：非无限分配模式下，计算预分配量的90%与预订单需求量（OpenQuantity+ReleasedQuantity+ShippedQuantity）的最大值，将该值赋值给内部创建的orderAllocationInput.PreorderAllocation字段后，调用ItemDao.SavePreorderAllocation。但当方法逻辑被修改为仅取90%预分配量时，现有NUnit单元测试未能自动失败，需在不修改原方法体的前提下调整测试断言，使其能检测到这类逻辑变更。

现有代码分析 #

原SaveOrderAllocation方法核心逻辑 #

public SaveActionResultWithCustomizedErrors<int> SaveOrderAllocation(OrderAllocation orderAllocation, FillOrderOutput fillOrderOutput)
{
    var saveResult = new SaveActionResultWithCustomizedErrors<int>();
    int? maxOfNinetyPercentAllocationQty = null;
    var title = new orderAllocationInput() {Ean = orderAllocation.Ean}; 

    try
    {
        if (!orderAllocation.IsUnlimitedAllocation)
        {
            if (orderAllocation.PreorderAllocationQty != null &
                orderAllocation.PreorderAllocationQty.HasValue)
            {
                var preDemandQty = (fillOrderOutput.OpenQuantity + fillOrderOutput.ReleasedQuantity + fillOrderOutput.ShippedQuantity);
                maxOfNinetyPercentAllocationQty = Math.Max(.9 * orderAllocation.PreorderAllocationQty.Value, preDemandQty).RoundToInt();
            }

            if (maxOfNinetyPercentAllocationQty != null) title.PreorderAllocation = maxOfNinetyPercentAllocationQty.Value;
        }
       
        ItemDao.SavePreorderAllocation(orderAllocation, fillOrderOutput);
        saveResult.SuccessfulItems.Add(orderAllocation.SystemId, orderAllocation.SystemId);
    }
    // 省略异常处理等代码
}

现有单元测试代码 #

[Test]
public void SaveOrderAllocation_With_OrderAllocationToMaxOf90Percent_Or_PreDemandQtyTest()
{
    // Arrange
    var orderAllocation = new OrderAllocation
    {
        Ean = "EAN123",
        Sysid = 1,
        PreorderAllocationQty = 100,
        IsUnlimitedAllocation = false
    };

    var fillOrderOutput = new FillOrderOutput
    {
        OpenQuantity = 80,
        ReleasedQuantity = 30,
        ShippedQuantity = 20
    };

    var preDemandQty = fillOrderOutput.OpenQuantity + fillOrderOutput.ReleasedQuantity + fillOrderOutput.ShippedQuantity;
    var expected = Math.Max(.9 * orderAllocation.PreorderAllocationQty.Value, preDemandQty).RoundToInt();

    // Act
    var result = Testee.SaveOrderAllocation(orderAllocation, fillOrderOutput);

    // Assert
    _itemDaoMock.Verify(x => x.SavePreorderAllocation(orderAllocation, fillOrderOutput), Times.Once());

    Assert.IsTrue(result.Success);
    Assert.That(result.FailedItems.Count, Is.EqualTo(0));
    Assert.That(result.SuccessfulItems.Count, Is.EqualTo(1));
    Assert.AreEqual(expected, preDemandQty);  // 这行断言完全无效
}

测试失效原因 #

现有测试存在两个关键问题：

• 无效断言：Assert.AreEqual(expected, preDemandQty)中，expected是按原逻辑计算的130，而preDemandQty本身就是测试代码中硬算的130，与方法内部的计算逻辑完全无关，无论方法逻辑怎么改，这行断言永远成立。
• 未验证核心逻辑：测试只验证了SavePreorderAllocation的调用次数，却没验证方法核心计算结果（即title.PreorderAllocation的值）是否被正确传递给了DAO层。

解决方案 #

调整测试逻辑，通过Mock验证SavePreorderAllocation被调用时，传入的参数中包含符合原逻辑的预期值。由于原方法中title是内部创建的，需通过参数匹配器验证其属性：

调整后的单元测试代码 #

[Test]
public void SaveOrderAllocation_With_OrderAllocationToMaxOf90Percent_Or_PreDemandQtyTest()
{
    // Arrange
    var orderAllocation = new OrderAllocation
    {
        Ean = "EAN123",
        Sysid = 1,
        PreorderAllocationQty = 100,
        IsUnlimitedAllocation = false
    };

    var fillOrderOutput = new FillOrderOutput
    {
        OpenQuantity = 80,
        ReleasedQuantity = 30,
        ShippedQuantity = 20
    };

    var preDemandQty = fillOrderOutput.OpenQuantity + fillOrderOutput.ReleasedQuantity + fillOrderOutput.ShippedQuantity;
    var expectedPreorderAllocation = Math.Max(.9 * orderAllocation.PreorderAllocationQty.Value, preDemandQty).RoundToInt();

    // Act
    var result = Testee.SaveOrderAllocation(orderAllocation, fillOrderOutput);

    // Assert
    // 验证DAO方法被调用时，传入的orderAllocationInput（即title）的PreorderAllocation等于预期值
    // 若SavePreorderAllocation实际接收OrderAllocation作为第一个参数，需调整匹配器验证对应属性
    _itemDaoMock.Verify(x => x.SavePreorderAllocation(
        It.Is<orderAllocationInput>(input => input.PreorderAllocation == expectedPreorderAllocation),
        fillOrderOutput), 
    Times.Once());

    // 保留基础结果断言
    Assert.IsTrue(result.Success);
    Assert.That(result.FailedItems.Count, Is.EqualTo(0));
    Assert.That(result.SuccessfulItems.Count, Is.EqualTo(1));
}

关键调整说明 #

• 移除了无效的Assert.AreEqual(expected, preDemandQty)断言。
• 修改_itemDaoMock.Verify，使用It.Is<T>参数匹配器，验证传入SavePreorderAllocation的orderAllocationInput对象的PreorderAllocation字段值是否符合原逻辑的预期值。
• 如果原方法中SavePreorderAllocation的第一个参数是OrderAllocation，且方法内部将title.PreorderAllocation赋值给了orderAllocation的对应属性，则将匹配器改为验证OrderAllocation的该属性值。

这样修改后，当SaveOrderAllocation的计算逻辑被改为仅取90%预分配量时，expectedPreorderAllocation会是130，而实际传入DAO的PreorderAllocation会是90，Mock验证会失败，测试就能正确检测到逻辑变更。

内容的提问来源于stack exchange，提问作者Sandy