Verifying calls

Count the requests

RequestCounter counts the requests the mock received, in total and per endpoint. It is a service of the mock: get it from Application.Services to check the number of calls once the code under test has run.

await using var mock = new HttpClientMock();
mock.MapGet("/status", () => "ok");
mock.MapPost("/events", () => Results.Accepted());

using var httpClient = mock.CreateHttpClient();
_ = await httpClient.GetStringAsync(new Uri("/status", UriKind.Relative));
using var response = await httpClient.PostAsync(new Uri("/events", UriKind.Relative), content: null);

// RequestCounter is a singleton of the mock's service provider
var counter = mock.Application.Services.GetRequiredService<RequestCounter>();
Assert.Equal(2, counter.TotalCount);

TotalCount counts every request, including the ones that match no endpoint.

Return a different response on each call

A handler can take the RequestCounter as a parameter. Get() returns the number of requests received by the endpoint that handles the current request:

await using var mock = new HttpClientMock();

// The first call fails and the next ones succeed, to test the retry logic of the code under test
mock.MapGet("/flaky", (RequestCounter counter) => counter.Get() is 1 ? Results.StatusCode(503) : Results.Ok("success"));

using var httpClient = mock.CreateHttpClient();
using var first = await httpClient.GetAsync(new Uri("/flaky", UriKind.Relative));
Assert.Equal(HttpStatusCode.ServiceUnavailable, first.StatusCode);

using var second = await httpClient.GetAsync(new Uri("/flaky", UriKind.Relative));
Assert.Equal(HttpStatusCode.OK, second.StatusCode);

A request is counted before its handler runs: in the handler, Get() returns 1 for the first request. A request whose handler throws is counted too.

Get(HttpContext) and Get(Endpoint) return the count of another endpoint, from the HttpContext of one of its requests or from the endpoint itself.

Capture the requests

To check what the client sent, such as a header, a query string or a body, store it from the handler and assert on it after the call:

await using var mock = new HttpClientMock();
var authorizationHeaders = new ConcurrentQueue<string>();
mock.MapGet("/me", (HttpRequest request) =>
{
    authorizationHeaders.Enqueue(request.Headers.Authorization.ToString());
    return "John";
});

using var httpClient = mock.CreateHttpClient();
httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", "token");
_ = await httpClient.GetStringAsync(new Uri("/me", UriKind.Relative));

Assert.Equal(["Bearer token"], authorizationHeaders.ToArray());

The mock can handle several requests at the same time: use a thread-safe collection, such as ConcurrentQueue<T>, when the code under test sends requests in parallel.