ReSharper Unit Test not run in bin directory

You don't list any version of NUnit installed, but you tagged this 'nunit' so I'm going to make an assumption you are using it! Further, I'm assuming NUnit >= 3.0... ignore this if otherwise. :-)

NUnit 3.0 stopped changing current directory. It's a bad idea for us to do that anyway and it's a really bad idea with 3.0, when multiple assemblies in differing directories may be running at the same time.

So, assuming still it's an NUnit problem, instead of using a relative path, use TestContext.CurrentContext.TestDirectory as the location of your file.

In my case was fixed when I changed to this setting

try this:

Directory.SetCurrentDirectory(AppDomain.CurrentDomain.BaseDirectory);