def box(request):
    """
    Parametrized fixture determining whether/how to transform fill_value.

    Since fill_value is defined on a per-test basis, the actual transformation
    (based on this fixture) is executed in _check_promote.

    Returns
    -------
    boxed : Boolean
        Whether fill_value should be wrapped in an np.array.
    box_dtype : dtype
        The dtype to pass to np.array([fill_value], dtype=box_dtype). If None,
        then this is passed on unmodified, and corresponds to the numpy default
        dtype for the given fill_value.

    * (True, None)    # fill_value wrapped in array with default dtype
    * (True, object)  # fill_value wrapped in array with object dtype
    * (False, None)   # fill_value passed on as scalar
    """
    return request.param