We want to make sure that file returns work

Let's register a view that returns a temporary file and make sure that
nothing bad happens. :)

    >>> from zope import component, interface
    >>> from zope.app.wsgi.testing import FileView
    >>> component.provideAdapter(FileView, name='test-file-view.html')
    >>> from zope.security import checker
    >>> checker.defineChecker(
    ...     FileView,
    ...     checker.NamesChecker(['browserDefault', '__call__']),
    ...     )

    >>> from webtest.app import TestApp
    >>> browser = TestApp(wsgi_app, extra_environ={'wsgi.handleErrors': False})
    >>> res = browser.get('http://localhost/@@test-file-view.html')
    >>> res.headers['content-type']
    'text/plain'

    >>> res.headers['content-length']
    '13'

    >>> print(res.body.decode())
    Hello
    World!
    <BLANKLINE>

Clean up:

    >>> import zope.publisher.interfaces.browser
    >>> checker.undefineChecker(FileView)
    >>> component.provideAdapter(
    ...     None,
    ...     (interface.Interface,
    ...     zope.publisher.interfaces.browser.IBrowserRequest),
    ...     zope.publisher.interfaces.browser.IBrowserPublisher,
    ...     'test-file-view.html',
    ...     )
