def _test_merge_next_block(ircfg, loc_key):
    """
    Test if the irblock at @loc_key can be merge with its son
    @ircfg: IRCFG instance
    @loc_key: LocKey instance of the candidate parent irblock
    """
    if loc_key not in ircfg.blocks:
        return None
    sons = ircfg.successors(loc_key)
    if len(sons) != 1:
        return None
    son = list(sons)[0]
    if ircfg.predecessors(son) != [loc_key]:
        return None
    if son not in ircfg.blocks:
        return None
    return son
