Test test_writer_bad_message fails with ujson

[jelly]

====================================== FAILURES ======================================
______________________________ test_writer_bad_message _______________________________

wfile = <_io.BytesIO object at 0x7f76043e6d60>
writer = <pylsp_jsonrpc.streams.JsonRpcStreamWriter object at 0x7f760392a8e0>

    def test_writer_bad_message(wfile, writer):
        # A datetime isn't serializable(or poorly serializable),
        # ensure the write method doesn't throw, but the result could be empty
        # or the correct datetime
        datetime.datetime = JsonDatetime
        writer.write(datetime.datetime(
            year=2019,
            month=1,
            day=1,
            hour=1,
            minute=1,
            second=1,
        ))

>       assert wfile.getvalue() in [
            b'',
            b'Content-Length: 10\r\n'
            b'Content-Type: application/vscode-jsonrpc; charset=utf8\r\n'
            b'\r\n'
            b'1546304461',
            b'Content-Length: 10\r\n'
            b'Content-Type: application/vscode-jsonrpc; charset=utf8\r\n'
            b'\r\n'
            b'1546322461'
        ]
E       AssertionError: assert b'Content-Length: 10\r\nContent-Type: application/vscode-jsonrpc; charset=utf8\r\n\r\n1546300861' in [b'', b'Content-Length: 10\r\nContent-Type: application/vscode-jsonrpc; charset=utf8\r\n\r\n1546304461', b'Content-Length: 10\r\nContent-Type: application/vscode-jsonrpc; charset=utf8\r\n\r\n1546322461']
E        +  where b'Content-Length: 10\r\nContent-Type: application/vscode-jsonrpc; charset=utf8\r\n\r\n1546300861' = <built-in method getvalue of _io.BytesIO object at 0x7f76043e6d60>()
E        +    where <built-in method getvalue of _io.BytesIO object at 0x7f76043e6d60> = <_io.BytesIO object at 0x7f76043e6d60>.getvalue

test/test_streams.py:118: AssertionError
============================== short test summary info ===============================
FAILED test/test_streams.py::test_writer_bad_message - AssertionError: assert b'Con...
============================ 1 failed, 26 passed in 0.10s ============================