:-1: :+1: :-1:  ... :+1: 

At first thought I preferred the security of the `try-except` block. However, I'm sold on the conditional `if tests.MPL_AVAILABLE:` block as a replacement as it's providing the context to the conditional import and the `try-except` block within `iris.tests` is checking **once** for the `ImportError` ... so, yeah, go for it @dkillick !