'Directories in the ``admin/build_targets/`` sub-directory of the path
passed to ``available_distributions`` which themselves contain a
``Dockerfile`` are considered distributions and included in the result.'

def test_dockerfiles(self):

    root = FilePath(self.mktemp())
    build_targets = root.descendant(['admin', 'build_targets'])
    build_targets.makedirs()
    build_targets.child('foo').setContent('bar')
    greatos = build_targets.child('greatos')
    greatos.makedirs()
    greatos.child('Dockerfile').setContent('MAINTAINER    example@example.invalid\n')
    nothing = build_targets.child('nothing')
    nothing.makedirs()
    self.assertEqual({'greatos'}, available_distributions(root))
