Maintaining complete calmness at all costs all the time is a bad ideal to strive for. Many people are more effective under pressure if they let their emotions affect them to an extend. Like Nynaeve. She did the weaves fine under huge pressure, so who cares if her emotions weren't totally under her rational control.

Another problem with the test and even more with the the Accepted test, is that the person who gets tested should demonstrate complete dedication to the White Tower and put everything else aside. Competence is a secondary criteria. Instead of sorting who's competent or not, those tests promotes those who are brainwashed enough by the Tower indoctrination to be ready to become yet another selfish manipulative Aes Sedai who couldn't care less about making the world a better place or doing anything worthwhile except furthering the political goals of the Tower or her own standing among the Aes Sedai.

The Aes Sedai as an organisation are obsessed a maintaining an appearance of competence and being in control instead of trying to prepare their members to be actually competent and in control. This test is just one of the many examples of it.

And as DomA said, the test makes no sense at all for most Ajah, since chances are they won't ever be asked to channel under extreme pressure and they need different qualities to be successful in their job.