Wait ... wasn't that 'Keep your tests green'? Of course I agree, if 50% of your tests are red all the time you have a problem. BUT if 100% of the tests are green all the time, then how do you know they can actually detect the errors they are supposed to cover? Simple answer you don't.

It really sounds like a trivial thing, but it isn't. So far I have three times accountered scenarios where tests couldn't possibly become red. And in all cases this went undetected at least for some time:

All cases where pretty trivial to fix, but also in all cases the not excecuted tests surfaced some problem when they where finally executed. So do yourself a favor and make sure that

And only than make sure that your tests stay green.