Domain Issues with NetworkCredential class in C#

On Friday we had some interesting issues related to the NetworkCredential class.

We were implementing some functionality that was very similar to an already existing piece of functionality, in essence we were calling a third party web service that required authentication. In reality is not a third party as we have the code for it, but it's for a different application, so for all intents and purposes we treat it as a third part service, i.e. it's a black box.

Since we had some unit tests for this call, we ran through them and we found an issue, it would not authenticate to the web service, so the test would fail. 

We checked through the application and the web service was working fine, which should have led us to believe that there was something wrong with the unit tests, but we assumed that the unit tests were working before and it was something environmental that was causing the issue.

As it turns out somebody had changed the unit tests and not bothered to test them. The issue was the following:

var cred=new NetworkCredential(@"dev\testuser", "ReallySecurePass1"); 

instead of:

var cred=new NetworkCredential("testuser", "ReallySecurePass1","dev");