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在 ASP.NET Core 单元测试中模拟HttpClient.GetStringAsync() 的测试技巧。
问题
下面这个代码
var html = await _httpClient.GetStringAsync(sourceUrl); 如果按正常思路像这样去 Mock HttpClient.GetStringAsync()
var httpClientMock = new Mock<HttpClient>(); httpClientMock .Setup(p => p.GetStringAsync(It.IsAny<string>())) .Returns(Task.FromResult("...")); Moq 框架就会爆
Exception
System.NotSupportedException : Unsupported expression: p => p.GetStringAsync(It.IsAny())Non-overridable members (here: HttpClient.GetStringAsync) may not be used in setup / verification expressions. 解决方法
我们需要 Mock HttpClient 底层使用的亿华云计算单元 HttpMessageHandler 而不是 HttpClient
var handlerMock = new Mock<HttpMessageHandler>(); var magicHttpClient = new HttpClient(handlerMock.Object); 然后我花了 9.96 分钟研究了 HttpClient.GetStringAsync() 的源代码，发现它最终调用的测试是服务器托管 SendAsync() 方法
private async Task<string> GetStringAsyncCore(HttpRequestMessage request, CancellationToken cancellationToken) { // ... response = await base.SendAsync(request, cts.Token).ConfigureAwait(false); // ... } 源代码位置：https://source.dot.net/#System.Net.Http/System/Net/Http/HttpClient.cs,170
因此，我们的单元 Mock Setup 如下：
handlerMock .Protected() .Setup<Task<HttpResponseMessage>>( "SendAsync", ItExpr.IsAny<HttpRequestMessage>(), ItExpr.IsAny<CancellationToken>() ) .ReturnsAsync(new HttpResponseMessage { StatusCode = HttpStatusCode.OK, Content = new StringContent("the string you want to return") }) .Verifiable(); 现在 Mock 就能运行成功了!
最后附上完整的 UT 代码供参考：
using System.Net; using System.Net.Http; using System.Threading; using System.Threading.Tasks; using Microsoft.Extensions.Logging; using Moq; using Moq.Protected; using NUnit.Framework; namespace Moonglade.Pingback.Tests { [TestFixture] public class PingSourceInspectorTests { private MockRepository _mockRepository; private Mock<ILogger<PingSourceInspector>> _mockLogger; private Mock<HttpMessageHandler> _handlerMock; private HttpClient _magicHttpClient; [SetUp] public void SetUp() { _mockRepository = new(MockBehavior.Default); _mockLogger = _mockRepository.Create<ILogger<PingSourceInspector>>(); _handlerMock = _mockRepository.Create<HttpMessageHandler>(); } private PingSourceInspector CreatePingSourceInspector() { _magicHttpClient = new(_handlerMock.Object); return new(_mockLogger.Object, _magicHttpClient); } [Test] public async Task ExamineSourceAsync_StateUnderTest_ExpectedBehavior() { string sourceUrl = "https://996.icu/work-996-sick-icu"; string targetUrl = "https://greenhat.today/programmers-special-gift"; _handlerMock .Protected() .Setup<Task<HttpResponseMessage>>( "SendAsync", ItExpr.IsAny<HttpRequestMessage>(), ItExpr.IsAny<CancellationToken>() ) .ReturnsAsync(new HttpResponseMessage { StatusCode = HttpStatusCode.OK, Content = new StringContent($"<html>" + $"<head>" + $"<title>Programmers Gift</title>" + $"</head>" + $"<body>Work 996 and have a <a href=\"{ targetUrl}\">green hat</a>!</body>" + $"</html>") }) .Verifiable(); var pingSourceInspector = CreatePingSourceInspector(); var result = await pingSourceInspector.ExamineSourceAsync(sourceUrl, targetUrl); Assert.IsFalse(result.ContainsHtml); Assert.IsTrue(result.SourceHasLink); Assert.AreEqual("Programmers Gift", result.Title); Assert.AreEqual(targetUrl, result.TargetUrl); Assert.AreEqual(sourceUrl, result.SourceUrl); } } }