Why Explict Invocation of Callback is Needed in setUp and tearDown?

I got to know nodeunit by reading this article http://caolanmcmahon.com/posts/unit_testing_in_node_js which should been written when nodeunit is at earlier phase. It doesn't mention that explicit invocation of callback function in setUp and tearDown.

There is no documentation about which arguments should be sent by invoking callback in setUp and tearDown. So, I suppose, in most cases, callback is just invoked without any arguments.

Why bother to require explicit invocation of this callback? can't it just be invoked by the system after setUp and tearDown is invoked?

Thanks,
-Morgan

Read the linked article and compare its setup and teardown examples with nodeunit's current documentation. Determine which callback arguments and invocation behavior need explanation, then document the rationale and expected usage; no specific file or test is named in the issue.

Written by the indexing model from the issue text.