def set_up_glove(url: str, byt: bytes, change_etag_every: int = 1000):
    # Mock response for the datastore url that returns glove vectors
    responses.add(
        responses.GET,
        url,
        body=byt,
        status=200,
        content_type="application/gzip",
        stream=True,
        headers={"Content-Length": str(len(byt))},
    )

    etags_left = change_etag_every
    etag = "0"

    def head_callback(_):
        """
        Writing this as a callback allows different responses to different HEAD requests.
        In our case, we're going to change the ETag header every `change_etag_every`
        requests, which will allow us to simulate having a new version of the file.
        """
        nonlocal etags_left, etag
        headers = {"ETag": etag}
        # countdown and change ETag
        etags_left -= 1
        if etags_left <= 0:
            etags_left = change_etag_every
            etag = str(int(etag) + 1)
        return (200, headers, "")

    responses.add_callback(responses.HEAD, url, callback=head_callback)
Writing this as a callback allows different responses to different HEAD requests.
In our case, we're going to change the ETag header every `change_etag_every`
requests, which will allow us to simulate having a new version of the file.
tests/common/file_utils_test.py