单元测试 Polly - 检查是否在超时/错误时触发重试策略

Question

问题 stmt：由于服务器问题，我有一个服务有时会从 graphql 获取结果，该服务可能会抛出 500 错误

解决方案：为了解决上述问题，我需要编写一个重试逻辑来在发生超时时重试服务。

障碍：我不知道如何断言给定的逻辑是否按照指定的方式调用了服务 3 次。任何帮助表示赞赏。

我创建了一个重试策略，以在给定客户端超时后重试。

public override void ConfigureServices(IServiceCollection services)
{
  services.AddHttpClient<GraphQueryService>(Constants.PPQClient)
        .ConfigureHttpClient(client =>
        {
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            client.Timeout = TimeSpan.FromMilliseconds(Constants.ClientTimeOut);
        }).AddRetryPolicy();
}

重试逻辑：

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Options;
using Polly;

namespace PA.Com.Integration
{
    public static class HttpClientBuilderExtensions
    {
        public static IHttpClientBuilder AddRetryPolicy(this IHttpClientBuilder builder)
        {
            var serviceProvider = builder.Services.BuildServiceProvider();

            var options = serviceProvider.GetRequiredService<IOptions<RetryOptions>>();

            return builder.AddTransientHttpErrorPolicy(b => b.WaitAndRetryAsync(new[]
            {
                options.Value.RetryDelay1,
                options.Value.RetryDelay2,
                options.Value.RetryDelay3
            }));
        }
    }
}

我是单元测试的新手，我相信我调用了代码来检查超时，但不确定如何断言它是否在超时时被调用了三次。

我试过的单元测试：

[Fact]
public async Task Check_Whether_Given_Policy_Executed_OnTimeout()
{
    // Given / Arrange 
    IServiceCollection services = new ServiceCollection();

    bool retryCalled = false;

    HttpStatusCode codeHandledByPolicy = HttpStatusCode.InternalServerError;

   var data =  services.AddHttpClient<GraphQueryService>(Constants.PPQClient)
            .ConfigureHttpClient(client =>
            {
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                client.Timeout = TimeSpan.FromMilliseconds(Constants.ClientTimeOut);
            }).AddRetryPolicy()
    .AddHttpMessageHandler(() => new StubDelegatingHandler(codeHandledByPolicy));

 //Need to Check the retry logic is called three times. Not sure How to continue after this.

    Assert.Equal(codeHandledByPolicy, HttpStatusCode.InternalServerError);
    Assert.True(retryCalled);
}

Answer 1

很遗憾，您无法创建单元测试来确保您的政策已正确设置。例如，在您设置重试次数和睡眠持续时间后，您将无法查询它们。

阅读 Polly 的源代码后，我找到了一个解决方案，但它非常脆弱，因为它依赖于 private 字段。我已经提出了a ticket，它将在 V8 中解决。 （何时发布存在很大的不确定性。）

---

那么，你能做什么？好吧，您可以在模拟下游 http 服务的地方编写集成测试。为此，我选择了 WireMock.Net 库。

我在下游系统上创建了两个抽象：

FlawlessService

internal abstract class FlawlessServiceMockBase
{
    protected readonly WireMockServer server;
    private readonly string route;

    protected FlawlessServiceMockBase(WireMockServer server, string route)
    {
        this.server = server;
        this.route = route;
    }

    public virtual void SetupMockForSuccessResponse(IResponseBuilder expectedResponse = null, 
        HttpStatusCode expectedStatusCode = HttpStatusCode.OK)
    {
        server.Reset();

        var endpointSetup = Request.Create().WithPath(route).UsingGet();
        var responseSetup = expectedResponse ?? Response.Create().WithStatusCode(expectedStatusCode);

        server.Given(endpointSetup).RespondWith(responseSetup);
    }
}

和FautlyService

internal abstract class FaultyServiceMockBase
{
    protected readonly WireMockServer server;
    protected readonly IRequestBuilder endpointSetup;
    protected readonly string scenario;

    protected FaultyServiceMockBase(WireMockServer server, string route)
    {
        this.server = server;
        this.endpointSetup = Request.Create().WithPath(route).UsingGet();
        this.scenario = $"polly-setup-test_{this.GetType().Name}";
    }

    public virtual void SetupMockForFailedResponse(IResponseBuilder expectedResponse = null,
        HttpStatusCode expectedStatusCode = HttpStatusCode.InternalServerError)
    {
        server.Reset();

        var responseSetup = expectedResponse ?? Response.Create().WithStatusCode(expectedStatusCode);

        server.Given(endpointSetup).RespondWith(responseSetup);
    }

    public virtual void SetupMockForSlowResponse(ResilienceSettings settings, string expectedResponse = null)
    {
        server.Reset();

        int higherDelayThanTimeout = settings.HttpRequestTimeoutInMilliseconds + 500;

        server
            .Given(endpointSetup)
            .InScenario(scenario)
            //NOTE: There is no WhenStateIs
            .WillSetStateTo(1)
            .WithTitle(Common.Constants.Stages.Begin)
            .RespondWith(DelayResponse(higherDelayThanTimeout, expectedResponse));

        for (var i = 1; i < settings.HttpRequestRetryCount; i++)
        {
            server
                .Given(endpointSetup)
                .InScenario(scenario)
                .WhenStateIs(i)
                .WillSetStateTo(i + 1)
                .WithTitle($"{Common.Constants.Stages.RetryAttempt} #{i}")
                .RespondWith(DelayResponse(higherDelayThanTimeout, expectedResponse));
        }

        server
            .Given(endpointSetup)
            .InScenario(scenario)
            .WhenStateIs(settings.HttpRequestRetryCount)
            //NOTE: There is no WillSetStateTo
            .WithTitle(Common.Constants.Stages.End)
            .RespondWith(DelayResponse(1, expectedResponse));
    }

    private static IResponseBuilder DelayResponse(int delay) => Response.Create()
        .WithDelay(delay)
        .WithStatusCode(200);

    private static IResponseBuilder DelayResponse(int delay, string response) => 
        response == null 
            ? DelayResponse(delay) 
            : DelayResponse(delay).WithBody(response);
}

通过这两个类，您可以模拟良好和不良行为的下游系统。

• WireMock 服务器将在指定端口上本地运行（详细信息稍后会介绍），并在可配置的路由上侦听 GET 请求
• ResilienceSettings 只是一个简单的帮助类来存储超时和重试策略的配置值
• 在服务器出现故障的情况下，我们定义了一个scenario，它基本上是一个请求-响应对的序列
  • 为了测试重试策略，您可以指定中间步骤的数量
  • 在所有不成功的（中间）请求之后，WireMock 服务器将自身转换为 End 状态 (WithTitle(Common.Constants.Stages.End))，这就是您可以在集成测试中查询的内容

---

这是一个简单的测试，它将针对缓慢的下游系统发出请求（重试）。它失败了几次，但最后它成功了

[Fact]
public async Task GivenAValidInout_AndAServiceWithSlowProcessing_WhenICallXYZ_ThenItCallsTheServiceSeveralTimes_AndFinallySucceed()
{
    //Arrange - Proxy request
    HttpClient proxyApiClient = proxyApiInitializer.CreateClient();

    //Arrange - Service
    var xyzSvc = new FaultyXYZServiceMock(xyzServer.Value);
    xyzSvc.SetupMockForSlowResponse(resilienceSettings);

    //Act
    var actualResult = await CallXYZAsync(proxyApiClient);

    //Assert - Response
    const HttpStatusCode expectedStatusCode = HttpStatusCode.OK;
    actualResult.StatusCode.ShouldBe(expectedStatusCode);

    //Assert - Resilience Policy
    var logsEntries = xyzServer.Value.FindLogEntries(
        Request.Create().WithPath(Common.Constants.Routes.XYZService).UsingGet());
    logsEntries.Last().MappingTitle.ShouldBe(Common.Constants.Stages.End);
}

请注意proxyApiInitializer 是WebApplicationFactory<Startup> 派生类的一个实例。

最后，这就是初始化 WireMock 服务器的方法

private static Lazy<WireMockServer> xyzServer;

public ctor()
{
   xyzServer = xyzServer ?? InitMockServer(API.Constants.EndpointConstants.XYZServiceApi);
}

private Lazy<WireMockServer> InitMockServer(string lookupKey)
{
    string baseUrl = proxyApiInitializer.Configuration.GetValue<string>(lookupKey);
    return new Lazy<WireMockServer>(
        WireMockServer.Start(new FluentMockServerSettings { Urls = new[] { baseUrl } }));
}