Is there an easy way to detect if you're running in the context of a Visual Studio Test as opposed to debug or release?

Here's the scenario - we have a factory class that we use heavily throughout our existing codebase, and I figured instead of refactoring it out in each class so we can substitute the default factory with one that would return mock/fake objects, I could add something in the factory class itself to return those mock objects if it detects it's running in "test" mode.