c# - 如何对异常处理程序中间件进行单元测试

Question

我正在尝试使用自定义错误处理程序为我的 .NET Core 3 API 返回格式正确的异常。处理程序运行良好，我遇到的问题是编写适当的单元测试来测试处理程序。我为此注册了中间件，如下所示:

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IEnvService envService)
    {
        if (envService.IsNonProductionEnv())
        {
            app.UseExceptionHandler("/Error-descriptive");
        }
        else
        {
            app.UseExceptionHandler("/Error");
        }

        ...

     }

这是“错误描述”端点的代码:

    public IActionResult ErrorDescriptive()
    {
        if (!_env.IsNonProductionEnv())            
            throw new InvalidOperationException("This endpoint cannot be invoked in a production environment.");

        IExceptionHandlerFeature exFeature = HttpContext.Features.Get<IExceptionHandlerFeature>();

        return Problem(detail: exFeature.Error.StackTrace, title: exFeature.Error.Message);
     }

我正在处理的问题是这一行:

IExceptionHandlerFeature exFeature = HttpContext.Features.Get<IExceptionHandlerFeature>();

从单元测试的角度来看，我很难让它工作，因为(据我所知)这行代码从服务器获取了最新的异常。有没有办法可以在我的测试中以某种方式设置它从 HttpContext 获得的异常？此外，由于这是使用 HttpContext，我是否需要以某种方式合并它的模拟版本，例如 DefaultHttpContext？

Answer 1

您可以通过注入(inject) IHttpContextAccessor 来实现这一点。 Controller 中的界面。
这个接口(interface)提供了一个抽象来访问 HttpContext 对象，主要是在你的 web 库之外。

要使用它，您必须services.AddHttpContextAccessor();在您的启动文件中。
然后你可以将它注入(inject)你的 Controller 。

[ApiController]
public class ErrorController
{
    private readonly ILogger<ErrorController> logger;
    private readonly IHttpContextAccessor httpContextAccessor;

    public ErrorController(ILogger<ErrorController> logger, IHttpContextAccessor httpContextAccessor){
        this.logger = logger;
        this.httpContextAccessor = httpContextAccessor ?? throw new ArgumentNullException(nameof(httpContextAccessor));
    }
}

然后在您的方法中，您使用访问器接口(interface)中的 HttpContext 而不是基类。

[Route("/error-development")]
public IActionResult HandleErrorDevelopment() 
{
     var exceptionFeature = this.httpContextAccessor.HttpContext.Features.Get<IExceptionHandlerFeature>();
     var error = exceptionFeature.Error;
}

由于我们现在针对注入(inject)的接口(interface)工作，因此您可以在单元测试中模拟它。请记住，您必须模拟您正在调用的整个链。 (我在这个例子中使用 xUnit 和 Moq)。

public ErrorControllerTests() {
     this.httpContextAccessorMock = new Mock<IHttpContextAccessor>();
     this.httpContextMock = new Mock<HttpContext>();
     this.featureCollectionMock = new Mock<IFeatureCollection>();
     this.exceptionHandlerFeatureMock = new Mock<IExceptionHandlerFeature>();

     this.httpContextAccessorMock.Setup(ca => ca.HttpContext).Returns(this.httpContextMock.Object);
     this.httpContextMock.Setup(c => c.Features).Returns(this.featureCollectionMock.Object);
     this.featureCollectionMock.Setup(fc => fc.Get<IExceptionHandlerFeature>()).Returns(this.exceptionHandlerFeatureMock.Object);

     this.controller = new ErrorController(null, this.httpContextAccessorMock.Object);
}

[Fact]
public void HandleErrorDevelopment() {
    Exception thrownException;
    try{
        throw new ApplicationException("A thrown application exception");
    }
    catch(Exception ex){
        thrownException = ex;
    }
    this.exceptionHandlerFeatureMock.Setup(ehf => ehf.Error).Returns(thrownException);

    var result = this.controller.HandleErrorDevelopment();
    var objectResult = result as ObjectResult;
    Assert.NotNull(objectResult);
    Assert.Equal(500, objectResult.StatusCode);
    var problem = objectResult.Value as ProblemDetails;
    Assert.NotNull(problem);
    Assert.Equal(thrownException.Message, problem.Title);
    Assert.Equal(thrownException.StackTrace, problem.Detail);
}

重要信息 : 您不能使用 ControllerBase.Problem()方法。此实现依赖于 ControllerBase.HttpContext检索 ProblemDetailsFactory目的。

您可以在 source code 中看到它.由于您的单元测试没有设置上下文，它会抛出 NullReferenceException .

工厂无非是创建 ProblemDetails 的 helper 目的。您再次可以看到 Default implementation on GitHub .

我最终创建了自己的私有(private)方法来创建这个对象。

private ProblemDetails CreateProblemDetails(
     int? statusCode = null,
     string title = null,
     string type = null,
     string detail = null,
     string instance = null){

     statusCode ??= 500;
     var problemDetails = new ProblemDetails
     {
          Status = statusCode.Value,
          Title = title,
          Type = type,
          Detail = detail,
          Instance = instance,
     };

     var traceId = Activity.Current?.Id ?? this.httpContextAccessor.HttpContext?.TraceIdentifier;
     if (traceId != null)
     {
         problemDetails.Extensions["traceId"] = traceId;
     }

     return problemDetails;
}

完整的错误处理方法如下所示。

[Route("/error-development")]
public IActionResult HandleErrorDevelopment() {
      var exceptionFeature = this.httpContextAccessor.HttpContext.Features.Get<IExceptionHandlerFeature>();
      var error = exceptionFeature.Error;
      this.logger?.LogError(error, "Unhandled exception");
      var problem = this.CreateProblemDetails(title: error.Message, detail: error.StackTrace);
       return new ObjectResult(problem){
           StatusCode = problem.Status
       };
}

对于生产，我要么提供要向用户显示的通用消息，要么在代码中抛出一个自定义处理的异常，该异常已经具有要显示的用户友好消息。

if (error is HandledApplicationException)
{
    // handled exceptions with user-friendly message.
    problem = this.CreateProblemDetails(title: error.Message);
}
else {
    // unhandled exceptions. Provice a generic error message to display to the end user.
    problem = this.CreateProblemDetails(title: "An unexpected exception occured. Please try again or contact IT support.");
}