'Test for block type. Must be overridden by subclasses.
As the parser loops through processors, it will call the ``test``
method on each to determine if the given block of text is of that
type. This method must return a boolean ``True`` or ``False``. The
actual method of testing is left to the needs of that particular
block type. It could be as simple as ``block.startswith(some_string)``
or a complex regular expression. As the block type may be different
depending on the parent of the block (i.e. inside a list), the parent
etree element is also provided and may be used as part of the test.
Keywords:
* ``parent``: A etree element which will be the parent of the block.
* ``block``: A block of text from the source which has been split at
blank lines.'

def test(self, parent, block):

    pass
