A:初版

test/NetClient.Test/TestDoubles/StaticTokenProvider.cs

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+using System.Threading;
+using System.Threading.Tasks;
+using NetClient.Abstractions;
+
+namespace NetClient.Test.TestDoubles;
+
+public sealed class StaticTokenProvider : IAccessTokenProvider
+{
+    private readonly string? _token;
+
+    public StaticTokenProvider(string? token)
+    {
+        _token = token;
+    }
+
+    public Task<string?> GetTokenAsync(CancellationToken cancellationToken = default) => Task.FromResult(_token);
+}
+

test/NetClient.Test/TestDoubles/TestHttpMessageHandler.cs

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+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) };
+}

test/NetClient.Test/TestDoubles/TestJsonSerializer.cs

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+using System.IO;
+using System.Text.Json;
+using System.Threading;
+using System.Threading.Tasks;
+using NetClient.Abstractions;
+
+namespace NetClient.Test.TestDoubles;
+
+public sealed class TestJsonSerializer : IHttpContentSerializer
+{
+    private readonly JsonSerializerOptions _options;
+
+    public TestJsonSerializer(JsonSerializerOptions? options = null)
+    {
+        _options = options ?? new JsonSerializerOptions(JsonSerializerDefaults.Web);
+    }
+
+    public string ContentType => "application/json";
+
+    public Task SerializeAsync<T>(Stream stream, T? value, CancellationToken cancellationToken = default)
+        => JsonSerializer.SerializeAsync(stream, value, _options, cancellationToken);
+
+    public Task<T?> DeserializeAsync<T>(Stream stream, CancellationToken cancellationToken = default)
+        => JsonSerializer.DeserializeAsync<T>(stream, _options, cancellationToken).AsTask();
+}