The logger is implemented with a map using __FILE__ and __LINE__.
Using the defaut values means that the same counter is used for
all the streams. This is jeopardizing the test.

Is anyone who tried the tests before ?

Former version crashed in case of syntax error
(cf test_syntax_error.py)

This unit test shows that after a given number of run
of the same file, the error changes.
Unfortunately, this can not be automatically verified, since
the result is printed in the python error stream, and cannot be
redirected.