A:初版

test/NetClient.Test/TestDoubles/TestHttpMessageHandler.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Net;
+using System.Net.Http;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace NetClient.Test.TestDoubles;
+
+public sealed class TestHttpMessageHandler : HttpMessageHandler
+{
+    private readonly Func<HttpRequestMessage, Task<HttpResponseMessage>> _handler;
+    private int _calls;
+
+    public int Calls => _calls;
+
+    public TestHttpMessageHandler(Func<HttpRequestMessage, Task<HttpResponseMessage>> handler)
+    {
+        _handler = handler;
+    }
+
+    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+    {
+        Interlocked.Increment(ref _calls);
+        return await _handler(request);
+    }
+
+    public static HttpResponseMessage Json(HttpStatusCode code, string json)
+        => new(code) { Content = new StringContent(json, System.Text.Encoding.UTF8, "application/json") };
+
+    public static HttpResponseMessage Text(HttpStatusCode code, string text)
+        => new(code) { Content = new StringContent(text) };
+}