Logging and services

The mock is an ASP.NET Core application. Its constructors configure the logging and the services of that application.

Log to the test output

The logs of the mock, such as the requests it receives, help understand why a request did not match. With the Meziantou.Extensions.Logging.Xunit.v3 package, send them to the output of the current xUnit test:

// The logs of the mock are written to the output of the current xUnit test
using var loggerProvider = new XUnitLoggerProvider(TestContext.Current.TestOutputHelper);
await using var mock = new HttpClientMock(loggerProvider);
mock.MapGet("/", () => "ok");

using var httpClient = mock.CreateHttpClient();
Assert.Equal("ok", await httpClient.GetStringAsync(new Uri("/", UriKind.Relative)));

The constructors accept an ILoggerProvider or an ILogger. For more control, pass an Action<ILoggingBuilder>, for instance to set the minimum level:

using var loggerProvider = new XUnitLoggerProvider(TestContext.Current.TestOutputHelper);
await using var mock = new HttpClientMock(logging =>
{
    logging.AddProvider(loggerProvider);
    logging.SetMinimumLevel(LogLevel.Trace);
});

Without a logger, the mock logs nothing. To assert on logs, see Logging.

Add services and configuration

configureServices adds services to the application of the mock. Handlers get them as parameters, as in a minimal API. The mock does not read the configuration of the host: appsettings.json, the ASPNETCORE_* and DOTNET_* environment variables and the command line are ignored, so a mock behaves the same on every machine. Add the configuration it needs:

await using var mock = new HttpClientMock(configureLogging: null, configureServices: services =>
{
    var configuration = new ConfigurationBuilder()
        .AddInMemoryCollection(new Dictionary<string, string?> { ["Greeting"] = "Hello" })
        .Build();
    services.AddSingleton<IConfiguration>(configuration);
});

mock.MapGet("/greeting", (IConfiguration configuration) => configuration["Greeting"]);

The application of the mock runs in the Production environment, with the directory of the test assembly as content root.

Choose a constructor

A bare null matches several of these constructors, and does not compile. Name the argument to choose one: new HttpClientMock(configureLogging: null, configureServices: services => ...).

Startup errors

The mock starts when the first client or handler is created. When the application fails to start, for instance because a hosted service added with configureServices throws while starting, CreateHttpClient and CreateHttpMessageHandler throw that error.