What difficulties met in completion tests?

Difficulties test takers can have with completion tests are:

• In order to do well on the test, the test taker has to know the content that is being tested. Some clues might be found in the question or in other questions, but that would be the exception and not the norm.
• Spelling of the answers might be a factor, so not only would you need to know the answer, but spell it correctly, too.