'Fails if the specified environment variable is set.
The default error message can be overridden with the ``msg`` argument.'

def environment_variable_should_not_be_set(self, name, msg=None):

    value = get_env_var(name)
    if value:
        self._fail(msg, ("Environment    variable    '%s'    is    set    to    '%s'." % (name, value)))
    self._info(("Environment    variable    '%s'    is    not    set." % name))
