c# - 测试错误 : The 'async' operator lacks await operator

Question

我有一个单元测试来检查 null 参数。测试方法是这样的:

[TestMethod]
public async Task Test_NullParam()
{
    Mock<IAuth> mockAuth = new Mock<IAuth>();
    Task<AuthenticationResult> mockResult = null;

    await Assert.ThrowsExceptionAsync<ArgumentNullException>(async () =>
    {
        mockAuth
          .Setup(x => x.Authenticate(null, param2, param3, param4))
          .Returns(mockResult);
    });
}

在 (async () 下显示错误。

错误是:

The async lacks await operator

mockResult 显示:

Result is always null

** 已编辑 **

类代码如下:

  public async Task<AuthenticationResult> Authenticate(string param1, string param2, string param3, string param4)
    {
        try
        {
            var authContext = new AuthenticationContext(param1);
            if (authContext.TokenCache.ReadItems().Any()) authContext = new AuthenticationContext(authContext.TokenCache.ReadItems().First().Authority);
            var authResult = await
            authContext.AcquireTokenAsync(param2, param3, new Uri(param4), new PlatformParameters(PromptBehavior.Auto, false));
            return authResult;
        }
        catch (Exception)
        {
            return null;
        }
    }

Answer 1

您收到错误是因为您没有执行 await您传递给 ThrowsExceptionAsync 的 lambda 中的语句.

更重要的是，您似乎是在 lambda 中执行模拟设置，而不是实际执行您正在测试的方法。您应该将模拟移到 lambda 之外，并像这样在 lambda 中执行您正在测试的方法:

[TestMethod]
public async Task Test_NullParam()
{
    // create all of your mocks that are required to run this test
    Mock<IAuth> mockAuth = new Mock<IAuth>();
    Task<AuthenticationResult> mockResult = null;
    mockAuth
        .Setup(x => x.Authenticate(null, param2, param3, param4))
        .Returns(mockResult);

    // you actually need to create the concrete type you want to test
    // you shouldn't make a unit test that just uses mocks!

    // construct the concrete type and pass in any mocks that the 
    // object requires
    var objectToTest = new MyRealObject(mockAuth.Object);

    await Assert.ThrowsExceptionAsync<ArgumentNullException>(async () =>
    {
        // actually execute the real method here, the assertion
        // is expecting this method to throw an exception, and will
        // only pass if an exception is thrown
        await objectToTest.MyMethodAsync();
    });
}

请注意，如果您正在测试的方法不是异步的，您应该将单元测试更改为非异步的，并使用 Assert.ThrowsException相反。

编辑:

回应您关于模拟 Task 的评论, 如果你想模拟 Task返回 null AuthenticationResult ，您应该执行以下操作:

// declare the result
AuthenticationResult mockResult = null;

// set up the authenticate method to return the task
mockAuth
    .Setup(x => x.Authenticate(null, param2, param3, param4))
    .Returns(Task.FromResult(mockResult));

这里重要的部分是Task.FromResult .这会给你一个实际的 Task ，这将返回 null等待时，而不是 Task正在null本身。

如果你想使用 AuthenticationResult那不是空的，你会遇到问题，由于 AuthenticationResult没有公共(public)构造函数的类，除了实际运行一个真正的 Authenticate 请求之外，没有办法获得一个。开箱即用，AuthenticationResult不可模拟，这就是为什么@Nkosi 提供了一篇关于 using wrapper classes to make it mockable 的文章的链接.

编辑2

链接的博文似乎不完整，因为它没有包含所有需要的包装器类型，所以我决定自己制作它们，这样这个答案就可以完整了。

由于 StackOverflow 答案的字符限制限制，我不得不将文件放在 Github 上:https://github.com/DoctaJonez/DoctorJones.IdentityModel.Clients.ActiveDirectory/tree/master

添加这些类和接口(interface)后，您将能够执行以下操作:

// you can now mock authentication results, and set them up to 
// emulate whatever conditions you like
var mockResult = new Mock<IAuthenticationResultWrapper>();

// you'll need to use the IAuthenticationContextWrapper, so all the
// method signatures know about our new IAuthenticationResultWrapper
var mockAuth = new Mock<IAuthenticationContextWrapper>();

// here's how we mock the IAuthenticationContextWrapper to return our
// mocked IAuthenticationResultWrapper
mockAuth.Setup(x => x.Authenticate(null, param2, param3, param4))
        .Returns(Task.FromResult(mockResult.Object));