Testing `IO ()` functions capturing their stdout/stderr etc.

[LeventErkok]

This is essentially the same issue as reported in: #434

Since silently isn't thread-safe, end-users have few options here. Doctest (or doc-spec) can run output producing functions and test-them inline, so surely that technology can be ported to tasty?

In any case, would it be meaningful to add a facility to test IO () functions where their stdout acts as the test-output?

[Bodigrim]

Sounds useful, although I'm not sure it is easy / possible to implement in Tasty. The problem is that stdout is global, process-wide. One would have to force single-threaded test execution + add locks around progress / result reporting.

[LeventErkok]

I wonder how doctest/docspec handle this problem: https://github.com/phadej/cabal-extras/tree/master/cabal-docspec

It surely can run doctests in parallel, and these functions can in general do IO (). Perhaps the trick they use can be somehow ported?