之前一篇AspNetCore服务端读写浏览器Cookie里使用了HttpResponse.OnStarting()方法通过注册回调来实现往Response里写入cookie。本篇我们看一下如何对其进行单元测试。

测试HttpResponse.OnStarting()

对HttpResponse进行测试&验证，离不开HttpContext以及一个Mock HttpResponse。首先我们尝试Mock一个HttpContext，并且Http Request和Response都直接用Mock。

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var requestMock = new Mock<HttpRequest>();
var responseMock = new Mock<HttpResponse>();
var httpContextMock = new Mock<HttpContext>();

Mock HttpResponse.OnStarting()的Setup可以借助Moq Callback来获取最终调用的回调方法，并放在next里触发回调方法的调用[1]，代码如下：

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 Func<object, Task> callbackMethod = null;
_responseMock.Setup(m => m.OnStarting(It.IsAny<Func<object, Task>>(), It.IsAny<object>()))
    .Callback<Func<object, Task>, object>((func, obj) => callbackMethod = func);

RequestDelegate next = async context =>
{
    _isNextDelegateCalled = true;
    if (callbackMethod != null)
    {
        await callbackMethod.Invoke(_httpContextMock.Object);
    }
    else
    {
        await Task.CompletedTask;
    }
};

有了上面的Mock代码，下面的单元测试确实可以触发callback方法的调用了，但是测试却通不过，因为代码context.Response.Cookies.Append(targetCookieName, cookieString);将cookie写入response后，不管通过responseMock.Object.GetTypedHeaders().SetCookie还是_responseMock.Object.Headers["Set-Cookie"]都无法获取到cookie的值。

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[Fact]
public async Task TestUpsertCookieMiddleware_WhenRequestContainsTargetCookie_ShouldResponseContainsUpdatedCookie()
{
    // Given
    var cookieValueTest = "key1=val1";
    _requestCookieMock.Setup(m => m.TryGetValue("cookie11", out cookieValueTest)).Returns(true);
    
    var expectResponseCookie = WebUtility.UrlEncode("key1=val1&newKey=newVal");
    
    // When
    await _upsertCookieMiddleware.Invoke(_httpContextMock.Object);

    // Then
    _isNextDelegateCalled.Should().BeTrue();
    _responseMock.Object.GetTypedHeaders().SetCookie.First(c => c.Name.Value == "cookie11").Value.ToString()
        .Should().Contain(expectResponseCookie);
    
    // _responseMock.Object.Headers["Set-Cookie"].Should().Contain(expectResponseCookie);
}

因为上面的尝试无法让测试通过，我们不得不另寻他法。研究一番发现有个IHttpResponseFeature这样的接口也可以Mock Response的状态和信息[2]，然后通过HttpContext.Features.Set()将Mock的Respnose注入。那现在我们借助DefaultHttpContext，这样可以解决上面遇到的问题。其实Mock IHttpResponseFeature和Mock HttpResponse差不多，代码如下：

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var responseMock = new Mock<IHttpResponseFeature>();
_httpContextMock = new DefaultHttpContext();

// Mock HttpResponse
Func<object, Task> callbackMethod = null;
responseMock.Setup(m => m.OnStarting(It.IsAny<Func<object, Task>>(), It.IsAny<object>()))
    .Callback<Func<object, Task>, object>((func, obj) => callbackMethod = func);
responseMock.Setup(m => m.Headers).Returns(new HeaderDictionary());

_httpContextMock.Features.Set(responseMock.Object);

基于上面新的Mock代码，下面的单元测试代码就可以顺利通过了。

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[Fact]
public async Task TestUpsertCookieMiddleware_WhenRequestContainsTargetCookie_ShouldResponseContainsUpdatedCookie()
{
    // Given
    _httpContextMock.Request.Headers["Cookie"] = "cookie11=key1=val1";
    var expectResponseCookie = WebUtility.UrlEncode("key1=val1&newKey=newVal");
    
    // When
    await _upsertCookieMiddleware.Invoke(_httpContextMock);

    // Then
    _isNextDelegateCalled.Should().BeTrue();
    _httpContextMock.Response.GetTypedHeaders().SetCookie.First(c => c.Name.Value == "cookie11").Value.ToString()
        .Should().Contain(expectResponseCookie);
}

扩展

仔细看的话，上面单元测试的代码里直接通过 _httpContextMock.Request.Headers["Cookie"] = "cookie11=key1=val1"; 来设置Http Request的cookie值，这就是采用DefaultHttpContext带来的便捷。
那么是否可以直接Mock Request里的cookie呢，答案是肯定的，有个IRequestCookiesFeature接口[3]可以用来Mock，然后直接注入DefaultHttpContext。代码如下：

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_httpContextMock = new DefaultHttpContext();
var requestCookieFeatureMock = new Mock<IRequestCookiesFeature>();
var responseMock = new Mock<IHttpResponseFeature>();

_requestCookieCollectionMock = new Mock<IRequestCookieCollection>();
requestCookieFeatureMock.Setup(m => m.Cookies).Returns(_requestCookieCollectionMock.Object);
_httpContextMock.Features.Set(requestCookieFeatureMock.Object);

基于上面新的Mock代码，改造后的单元测试里直接Mock IRequestCookieCollection的TryGetValue[4], out值通过一个本地变量定义[5]，测试顺利通过。

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[Fact]
public async Task TestUpsertCookieMiddleware_WhenRequestContainsTargetCookie_ShouldResponseContainsUpdatedCookie()
{
    // Given
    var cookieKeyTest = "cookie11"; 
    var cookieValueTest = "key1=val1";
    
    _requestCookieCollectionMock.Setup(m => m.TryGetValue(cookieKeyTest, out cookieValueTest)).Returns(true);
    
    var expectResponseCookie = WebUtility.UrlEncode("key1=val1&newKey=newVal");
    
    // When
    await _upsertCookieMiddleware.Invoke(_httpContextMock);

    // Then
    _isNextDelegateCalled.Should().BeTrue();
    _httpContextMock.Response.GetTypedHeaders().SetCookie.First(c => c.Name.Value == cookieKeyTest).Value.ToString()
        .Should().Contain(expectResponseCookie);
}

除了本篇用到的IHttpResponseFeature、IRequestCookiesFeature，还有很多其他的Feature[6]，例如IHttpRequestFeature等，可以借助它们做很多其他事情。

另外，上面的单元测试里校验cookie时借助了WebUtility.UrlEncode，它和HttpUtility.UrlEncode略有不同[7]。WebUtility encode后的符号的编码是大写，而HttpUtility则是小写。
UrlEncode WebUtility vs HttpUtility

结语

在进行HttpContext相关的单元测试时，优先借助DefaultHttpContext可以减少很多不必要的Mock代码。尽量借助相关的Feature[6:1]来进行Mock，也会达到事半功倍的效果。

源码

Demo代码已上传 https://github.com/jeremyLJ/aspnetcore_read_write_cookie/tree/main/aspnetcore_read_write_cookie_demo/WebApiTest

  1. https://www.appsloveworld.com/csharp/100/302/how-to-unit-test-a-net-middleware-that-uses-response-onstarting ↩︎

  2. https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.http.features.ihttpresponsefeature ↩︎

  3. https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.http.features.irequestcookiesfeature ↩︎

  4. https://github.com/dotnet/aspnetcore/issues/18193#issuecomment-572938829 ↩︎

  5. https://www.codeproject.com/Articles/5286617/Moq-and-out-Parameter ↩︎

  6. https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.http.features ↩︎ ↩︎

  7. https://edi.wang/post/2018/11/25/netcore-webutility-urlencode-httputility-urlencode ↩︎