def METHOD_NAME(graph):
    """setDirty on Input should always modify OPs ._previous_dirty_mod_time"""
    op = MockOp(graph=graph)
    assert op._previous_dirty_mod_time == -1
    assert op._pending_dirty_mod_time == -1
    op.Input.setDirty(())
    assert op._previous_dirty_mod_time > -1