使用Moq统计C#递归方法SendMessage调用次数的异常问题

报错原因说明 #

• 非虚SendMessage无法Verify：Moq基于动态生成目标类子类、重写虚成员实现调用拦截，非虚成员无法被重写，自然不支持Setup/Verify操作，属于Moq的底层实现限制。
• 改为虚方法后仅统计到1次调用：未对虚SendMessage配置调用规则时，Moq默认不会走基类的递归逻辑，且内部调用未被代理拦截，导致计数缺失。

最优解决方案（无需修改SendMessage为virtual） #

你需要测试的核心逻辑是返回401时会重试发送请求，完全可以通过验证可重写的SendMessageUsingHttpClient的调用次数实现测试目标，无需调整原有业务方法的修饰符。

第一步：先修复业务代码的bug #

原有SendMessage递归调用后没有接收返回值，无论递归多少次都会返回第一次的401响应，修正后代码：

public HttpResponseMessage SendMessage(HttpRequestMessage httpRequestMessage, HttpStatusCode? httpStatusCode = null)
{
    GetRandomTokenAndAddInMessageHeader(httpRequestMessage, httpStatusCode);

    var response = SendMessageUsingHttpClient(httpRequestMessage);

    if (response.StatusCode == HttpStatusCode.Unauthorized)
    {
        // 接收递归调用的返回值，保证最终返回重试后的响应
        response = SendMessage(httpRequestMessage, HttpStatusCode.Unauthorized);
    }

    return response;
}

public virtual HttpResponseMessage SendMessageUsingHttpClient(HttpRequestMessage httpRequestMessage)
{
    return _httpClient.Send(httpRequestMessage, CancellationToken.None);
}

第二步：修改测试代码 #

[TestMethod]
public void Send_MustRetry_When_UnauthorizedReturned()
{
    var mockHttpResponseManager = new Mock<HttpRequestManager>();

    var expectedUnauthorizedResponse = new HttpResponseMessage { StatusCode = HttpStatusCode.Unauthorized };
    var expectedOkResponse = new HttpResponseMessage { StatusCode = HttpStatusCode.OK };

    mockHttpResponseManager.SetupSequence(m => m.SendMessageUsingHttpClient(It.IsAny<HttpRequestMessage>()))
        .Returns(expectedUnauthorizedResponse)
        .Returns(expectedOkResponse);

    var result = mockHttpResponseManager.Object.SendMessage(new HttpRequestMessage());

    // 验证最终返回重试后的200响应
    Assert.AreEqual(HttpStatusCode.OK, result.StatusCode);
    // 验证SendMessageUsingHttpClient被调用2次，说明触发了一次重试，完全满足测试需求
    mockHttpResponseManager.Verify(v => v.SendMessageUsingHttpClient(It.IsAny<HttpRequestMessage>()), Times.Exactly(2));
}

特殊场景方案：必须验证SendMessage调用次数 #

如果确实需要统计SendMessage的递归次数，可按如下方式实现：

第一步：将SendMessage改为virtual #

public virtual HttpResponseMessage SendMessage(HttpRequestMessage httpRequestMessage, HttpStatusCode? httpStatusCode = null)
{
    // 同上修正后的逻辑
}

第二步：修改测试代码，开启CallBase配置 #

[TestMethod]
public void Send_MustCall_Twice_When_UnauthorizedReturned()
{
    // 开启CallBase，未配置的虚方法默认调用基类实现
    var mockHttpResponseManager = new Mock<HttpRequestManager>() { CallBase = true };

    var expectedUnauthorizedResponse = new HttpResponseMessage { StatusCode = HttpStatusCode.Unauthorized };
    var expectedOkResponse = new HttpResponseMessage { StatusCode = HttpStatusCode.OK };

    mockHttpResponseManager.SetupSequence(m => m.SendMessageUsingHttpClient(It.IsAny<HttpRequestMessage>()))
        .Returns(expectedUnauthorizedResponse)
        .Returns(expectedOkResponse);

    // 显式配置SendMessage调用基类实现，保证递归逻辑正常执行且被拦截统计
    mockHttpResponseManager.Setup(m => m.SendMessage(It.IsAny<HttpRequestMessage>(), It.IsAny<HttpStatusCode?>()))
        .CallBase();

    mockHttpResponseManager.Object.SendMessage(new HttpRequestMessage());

    // 此时可正确统计到2次SendMessage调用
    mockHttpResponseManager.Verify(v => v.SendMessage(It.IsAny<HttpRequestMessage>(), It.IsAny<HttpStatusCode?>()), Times.Exactly(2));
}

内容的提问来源于stack exchange，提问作者Carolynne Padilha