qcheck: add OUnit2 test converter

[edwintorok]

To take advantage of OUnit2 features (parallel execution, html logging, etc.) tests need to be of type OUnit2.test.

to_ounit2_test:

• uses the same fixed random state (which can be overriden with "-seed" on the command-line)
• logs verbose info using OUnit2 logging function
• property check failures use assert_fail, to distinguish them from tests that raise exceptions (errors)

This is more complicated due to seed handling: OUnit2 only prints the exception / failure message by default (the other messages are logged), using an auto-generated random seed would be inconvenient:

• command-line arguments are only known at test run time, and printing the random seed at this time would either go to the log (were its inconvenient to quickly find it), or stdout/stderr (where it would be mixed with everything else and not known to which test it belongs). Also OUnit2 allows arguments to be specified in a config file, instead of command-line, so inspecting Sys.argv wouldn't be enough to know whether the user supplied a custom seed

[c-cube]

That looks pretty nice! I don't use OUnit2, but I understand the point. Could you please add a test file for this new function (e.g. copy and adapt tests/Runner_ounit_test.ml)?

[edwintorok]

Pushed the example, also added a convenience function for converting a list of tests to ounit2

[c-cube]

Thanks!