MockHttpMessageHandler.cs

using System;
using System.Collections.Generic;
using System.Net;
using System.Net.Http;
using System.Text.Json;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.VisualStudio.Services.Common;

namespace Pier8Software.TestingHelpers
{
    public class MockHttpMessageHandler : HttpMessageHandler
    {
        private readonly string response;
        private readonly HttpStatusCode statusCode;
        private readonly Dictionary<string, HttpResponseMessage> responses = new Dictionary<string, HttpResponseMessage>();
        private readonly Dictionary<string, HttpRequestMessage> requests = new Dictionary<string, HttpRequestMessage>();

        public void AddResponse(HttpMethod method, string endpoint, HttpResponseMessage response)
        {
            var key = GetKey(method, endpoint);
            responses.Add(key, response);
        }

        public async Task ValidateRequest<T>(HttpMethod method, string endpoint, Action<T> assert, JsonSerializerOptions serializerOptions)
        {
            var key = GetKey(method, endpoint);
            requests.TryGetValue(key, out var request);

            if (request != null)
            {
                var content = await request.Content.ReadAsStringAsync();
                var model = JsonSerializer.Deserialize<T>(content, serializerOptions);
                assert(model);
                return;
            }

            throw new Exception($"Validation Failed: Request to {endpoint} Not Found.");
        }

        public async Task ValidateRequest<T>(HttpMethod method, string endpoint, Action<T> assert)
        {
            await ValidateRequest<T>(method, endpoint, assert, new JsonSerializerOptions());
        }

        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request,
            CancellationToken cancellationToken)
        {
            var key = GetKey(request.Method, request.RequestUri.AbsolutePath);
            requests[key] = request;
            if (responses.TryGetValue(key, out var response))
            {
                return response;
            }
        }
        
        private string GetKey(HttpMethod method, string endpoint)
        {
            return $"{method.Method}-{endpoint}";
        }
    }
}