编写具有网络连接依赖性的方法的单元测试

Question

I am writing a Downloader (for fun with TDD), in that i have a method, whose responsibility is to connect to the file.

class FileConnectorHttp : IFileConnector
{
public void ConnectToFile()
{
  //creating a concrete web request here.
  HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(UriForTheFileToConnect);

  //sending HEAD request.
  webRequest.Method = "HEAD";

  //other logic for connection will go here.
  try
  {
    HttpWebResponse response = webRequest.GetResponse() as HttpWebResponse;

  }
  catch (ProtocolViolationException e)
  {
    throw;
  }
  catch (InvalidOperationException e)
  {

    throw;
  }

}
}

I wrote a test for testing the scenario of connection timeout.

[Test]
public void ConnectToSourceFile_ValidUri_Connection_TimeOut_Throws_WebException()
{
  Uri uriForTheFileToDownload = new Uri("https://suppose/this/is/valid/url.txt");

  FileConnectorHttp fileConnectorOverHttp = new FileConnectorHttp(uriForTheFileToDownload);

  Assert.Throws(Is.TypeOf<WebException>(),

    () => fileConnectorOverHttp.ConnectToFile());

}

So to get this exception should i turn off my Wifi connection? What should be the meaningful way to test for this kind of exception?

Answer 1

There is no reason for you to test that a failure to connect throws a WebException. It's not your code that is doing the throwing.

OTOH, you probably want to test at some point that your code properly handles a WebException when it is thrown . To do that, you will have to wrap or mock the underlying web request.

Answer 2

A Unit Test ideally should not rely on external dependancies like Network connections. As mentioned in the comment above (the link) you want to Mock this behaviour. Otherwise using a real connection you would not be able to test failure cases ie A good connection and no connection in an automated way.

Unit Tests should follow the FIRST acronym

• Fast
• Independent
• Repeatable
• Self-Validating
• Timely

If you need a test to actually use the physically connection, then you could write an Integration or System test - Maybe using BDD.

The benefits to this approach is that your unit test suite can run quickly (automated), cover many scenario's and give you very quick feedback. Whereas the Integration Test can be run less frequently (if desired) and you need not worry so much about how long they take, as all you are doing here is proving end-to-end connectivity.