DOC:Some minor proofreading of Tests introduction
DOC:Revert ``assert()`` back to ``assert`` (statement)
Merge pull request #3550 from endolith/patch-1

DOC:Some minor proofreading of Tests introduction
MAINT: typo fix in logging message

The logging message in numpy.distutils.log.set_threshold
mispelled threshold.
STY: Break long lines in numpy/distutils/log.py.