Feature request : Stop after n failed tests

[wizzup]

I would love to have command line argument for doctest binary to stop after specific number of failed tests.

The example use case is when I am doing coding exercise, for example fp-course, and only want to test on function I am currently working on.

My work-around for this is to redirect test output to head program.

$ doctest code.hs 2>&1 | head -n 10

The problem of this method is it will run all other tests wastefully.