Return error message from the check

[prikha]

There are multiple cases when you need to process the message manually e.g. custom test matcher or notificaiton.
It'd be cool to have an opportunity to get the error message instead of an exception.

[charkost]

Hello, your change seems pretty contained & would be accepted if the CI passes.

[prikha]

@charkost I need a bit more than a message so I went ahead with a re-write that matches my needs. Check your mail - I PM'ed you with a broader explanation.