如何在单元测试HttpClient时模拟GetDiscoveryDocumentAsync？

var discoveryEndpointMock = new Mock<IDiscoveryEndpoint>();
discoveryEndpointMock.Setup(e => e.GetDiscoveryDocumentAsync()).ReturnsAsync(new DiscoveryDocument());

var httpClient = new HttpClient(new DiscoveryEndpointHandler(discoveryEndpointMock.Object));

public class DiscoveryEndpointHandler : DelegatingHandler
{
    private readonly IDiscoveryEndpoint _discoveryEndpoint;

    public DiscoveryEndpointHandler(IDiscoveryEndpoint discoveryEndpoint)
    {
        _discoveryEndpoint = discoveryEndpoint;
    }

    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        if (request.RequestUri.AbsoluteUri.EndsWith("/.well-known/openid-configuration"))
        {
            var discoveryDocument = await _discoveryEndpoint.GetDiscoveryDocumentAsync();
            var response = new HttpResponseMessage(HttpStatusCode.OK);
            response.Content = new StringContent(JsonConvert.SerializeObject(discoveryDocument), Encoding.UTF8, "application/json");
            return response;
        }

        return await base.SendAsync(request, cancellationToken);
    }
}