def add_gctx_to_out_name(out_file_name):
    """
	If there isn't a '.gctx' suffix to specified out_file_name, it adds one.

	Input:
		- out_file_name (str): the file name to write gctx-formatted output to.
			(Can end with ".gctx" or not)

	Output:
		- out_file_name (str): the file name to write gctx-formatted output to, with ".gctx" suffix
	"""
    if not out_file_name.endswith(".gctx"):
        out_file_name = out_file_name + ".gctx"
    return out_file_name