Mocking HTTPResponse in a unit test

Question

I'm trying to create unit tests for some legacy code . One of the classes that I have to test is called FileDownloader which has just the following one method :

public void Transmit(string fileName, HttpResponse response, DownloadFileType fileType, byte[] content)
{
    response.Clear();
    response.ClearHeaders();
    response.ContentType = "application/xls";
    response.AddHeader("content-disposition", "attachment; filename=" + HttpContext.Current.Server.UrlEncode(fileName));
    response.BinaryWrite(content);
    response.End();
    response.Flush();
}

I'm not allowed to refactor this code ( which would have been ideal ! ).

To test this I decided to create a fake HttpContext based on the article below

Click this

With this I'm able to get a fake HttpContext during my test execution , however there are issues with faking the HttpResponse .

Here's how my test looks like :

[SetUp]
public void SetUp()
{
    mocks = new MockRepository();            
    FakeHttpContext.CreateFakeHttpContext();
}

[Test]
public void ShouldTransmitHttpResponseInTheSpecifiedFormat()
{
    FileDownloader downloader = new FileDownloader();
    string path = "..\\..\\Fakes\\DummyDownloadReportsTemplate.xls";
    byte[] bytes = ReadByteArrayFromFile(path);
    downloader.Transmit("test.xls", new HttpResponse(new StringWriter()), DownloadFileType.Excel, bytes);
}

I'm passing a custom created HTTPResponse object to the method. This throws the following exception when it hits the "response.BinaryWrite(content)" line :

System.Web.HttpException : OutputStream is not available when a custom TextWriter is used.

I'm not sure what exactly should I be asserting here .. hence there no asserts in the test. Is this the correct way to test this method ... any ideas . please advise ?

Thanks

Answer 1

Another way of testing it is using abstract base classes like HttpContextBase, HttpResponseBase, etc. http://msdn.microsoft.com/en-us/library/system.web.httpcontextbase(v=VS.90).aspx

HttpContextBase is a part of .NET 3.5 SP1, .NET 4.0 and can be installed as a separate package for .NET 2.0. When I was testing uploading/downloading handlers that feature had appeared a remedy for me :-).

Usage is simple. This method will be covered with test.

public void Transmit(string fileName, HttpResponseBase response, DownloadFileType fileType, byte[] content)
{
...
// main logic.
...
}

For the real context you can just create a stub and delegate to the testable method, like:

public void Transmit(string fileName, HttpResponse response, DownloadFileType fileType, byte[] content)
{
   var requestWrapper = new HttpResponseWrapper(response);
   this.Transmit(fileName, requestWrapper, fileType, content);
}