'Ensure prepare_headers regex isn\'t flagging valid header contents.'

def test_header_validation(self, httpbin):

    headers_ok = {'foo': 'bar    baz    qux', 'bar': u'fbbq'.encode('utf8'), 'baz': '', 'qux': '1'}
    r = requests.get(httpbin('get'), headers=headers_ok)
    assert (r.request.headers['foo'] == headers_ok['foo'])
