Currently the tests involving the msgpack codec expect broken behaviour where the codec converts an array of bytes objects to an array of str (unicode) objects. Relevant line of code is here:
https://github.com/zarr-developers/zarr/blob/a4d5656e3042216308b03ab7514567139d4004fc/zarr/tests/test_core.py#L985
This is causing problems elsewhere, e.g., #278 (comment).