Handle case where no tests was executed

[jlndk]

We might want some more useful output if no tests was executed.

This can happen if no tests has been written yet, a filter has been added to the test command where no tests match, or the --changedSince flag has been added to the test command.

Currently it looks like this:

We might also want a failOnNoTests flag or something like that, which fails if no tests where executed.