writing well integrated assertion helpers
========================================================

If you have a test helper function called from a test you can
use the ``pytest.fail`` marker to fail a test with a certain message.
The test support function will not show up in the traceback if you
set the ``__tracebackhide__`` option somewhere in the helper function.
Example::

    # content of test_checkconfig.py
    import pytest
    def checkconfig(x):
        __tracebackhide__ = True
        if not hasattr(x, "config"):
            pytest.fail("not configured: %s" %(x,))

    def test_something():
        checkconfig(42)

The ``__tracebackhide__`` setting influences py.test showing
of tracebacks: the ``checkconfig`` function will not be shown
unless the ``--fulltrace`` command line option is specified.
Let's run our little function::

    $ py.test -q
    F
    ================================= FAILURES =================================
    ______________________________ test_something ______________________________
    
        def test_something():
    >       checkconfig(42)
    E       Failed: not configured: 42
    
    test_checkconfig.py:8: Failed
    1 failed in 0.02 seconds