How to get Resharper to allow underscores in method names but only in Tests?

I know that there is a way to do this, but I can't find it again.

So, does any one know how to allow Resharper to allow underscores in unit tests?

So, for example I want this to be OK

In MyClassTest.cs

public void MyMethodName_StateUnderTest_ExpectedResult()
{}

But I want this to flag:

In MyClass.cs

public void MyPoorly_Named_Method()
{}

Thanks for any help