c# - 单元测试需要更多时间做减法

Question

我正在通过编写简单示例来尝试单元测试。

测试代码:

public class Operations
{
    public static double Subtraction(double number1, double number2)
    {
        return number1 - number2;
    }

    public static double Addition(double number1, double number2)
    {
        return number1 + number2;
    }

    public static double Division(double number1, double number2)
    {
        if (number2 != 0)
        {
            return number1 / number2;
        }
        else
        {
            return number1;
        }
    }

    public static double Multiplication(double number1, double number2)
    {
        return number1 * number2;
    }
}

测试方法:

[TestClass()]
public class OperationsTests
{
    [TestMethod()]
    public void SubtractionTest1()
    {
        double number1 = 0;
        double number2 = 10;
        double result = Operations.Subtraction(number1, number2);
        Assert.AreEqual(-10, result);
    }

    [TestMethod()]
    public void SubtractionTest2()
    {
        double number1 = 10;
        double number2 = 0;
        double result = Operations.Subtraction(number1, number2);
        Assert.AreEqual(10, result);
    }

    [TestMethod()]
    public void SubtractionTest3()
    {
        double number1 = 10;
        double number2 = 10;
        double result = Operations.Subtraction(number1, number2);
        Assert.AreEqual(0, result);
    }

    [TestMethod()]
    public void AdditionTest1()
    {
        double number1 = 0;
        double number2 = 10;
        double result = Operations.Addition(number1, number2);
        Assert.AreEqual(10, result);
    }

    [TestMethod()]
    public void AdditionTest2()
    {
        double number1 = 10;
        double number2 = 0;
        double result = Operations.Addition(number1, number2);
        Assert.AreEqual(10, result);
    }

    [TestMethod()]
    public void AdditionTest3()
    {
        double number1 = 10;
        double number2 = 10;
        double result = Operations.Addition(number1, number2);
        Assert.AreEqual(20, result);
    }

    [TestMethod()]
    public void DivisionTest1()
    {
        double number1 = 0;
        double number2 = 10;
        double result = Operations.Division(number1, number2);
        Assert.AreEqual(0, result);
    }

    [TestMethod()]
    public void DivisionTest2()
    {
        double number1 = 10;
        double number2 = 0;
        double result = Operations.Division(number1, number2);
        Assert.AreEqual(10, result);
    }

    [TestMethod()]
    public void DivisionTest3()
    {
        double number1 = 10;
        double number2 = 10;
        double result = Operations.Division(number1, number2);
        Assert.AreEqual(1, result);
    }

    [TestMethod()]
    public void MultiplicationTest1()
    {
        double number1 = 0;
        double number2 = 10;
        double result = Operations.Multiplication(number1, number2);
        Assert.AreEqual(0, result);
    }

    [TestMethod()]
    public void MultiplicationTest2()
    {
        double number1 = 10;
        double number2 = 0;
        double result = Operations.Multiplication(number1, number2);
        Assert.AreEqual(0, result);
    }

    [TestMethod()]
    public void MultiplicationTest3()
    {
        double number1 = 10;
        double number2 = 10;
        double result = Operations.Multiplication(number1, number2);
        Assert.AreEqual(100, result);
    }
}

每个测试都在执行，没有任何错误，但我注意到 SubtractionTest1 总是花费 7-8-9 毫秒，而其他测试花费不到 1 毫秒，你能解释一下为什么吗？

测试结果:

Answer 1

MSTest 将随机化单元测试的运行顺序，因为这有时会暴露计时或共享状态中的错误。

您首先运行的测试将花费更长的时间，因为它将是 JIT 编译您的每个方法和类型所必需的测试，并且如果这些类型中的任何一个具有要执行的静态初始化，那么这也会触发。

我有一个单元测试套件，其中第一个测试总是需要大约 0.5 秒，因为我正在初始化依赖注入(inject)和模拟框架。每个测试后初始化大约需要 1 毫秒到 2 毫秒。所以你在这里看到的行为是完全正常的。

对于性能测试，您必须对结果进行平均并丢弃第一个结果以从中删除初始化时间。如果这与您的应用程序相关，您还应该测试您的初始化速度，但它通常与启动一次然后保持在线并准备就绪的服务器无关。