polly3.cs

private static IAsyncPolicy<HttpResponseMessage> GetRetryPolicy()
{
    return HttpPolicyExtensions
        .HandleTransientHttpError()
        .OrResult(msg => msg.StatusCode == HttpStatusCode.ServiceUnavailable)
        .RetryAsync(3);
}

[Fact]
public async Task ShouldRetryTransientErrors()
{
    // Arrange
    int numberOfRequests = 0;
    var options = new HttpClientInterceptorOptions {ThrowOnMissingRegistration = true};
    new HttpRequestInterceptionBuilder()
        .Requests()
        .ForHttps()
        .ForHost("bbc.co.uk")
        .ForPath("/news")
        .Responds()
        .WithStatus(HttpStatusCode.ServiceUnavailable)
        .WithInterceptionCallback(_ => numberOfRequests++)
        .RegisterWith(options);

    var collection = new ServiceCollection()
        .AddHttpClient("bbc_client")
        .AddPolicyHandler(GetRetryPolicy())
        .AddHttpMessageHandler(options.CreateHttpMessageHandler)
        .Services
        .BuildServiceProvider();

    var httpClient =  collection.GetService<IHttpClientFactory>().CreateClient("bbc_client");

    // Act
    var response = await httpClient.GetAsync("https://bbc.co.uk/news");

    // Assert
    numberOfRequests.ShouldBe(4);
    response.StatusCode.ShouldBe(HttpStatusCode.ServiceUnavailable);
}