Verifies that a fake subpackage path for assets (notebooks, svgs,
    pngs etc) both exists and is populated with files.

def check_pseudo_package(path):
    """
    Verifies that a fake subpackage path for assets (notebooks, svgs,
    pngs etc) both exists and is populated with files.
    """
    if not os.path.isdir(path):
        raise Exception("Please make sure pseudo-package %s exists." % path)
    else:
        assets = os.listdir(path)
        if len(assets) == 0:
            raise Exception("Please make sure pseudo-package %s is populated." % path)