Tests like this test test your vocabulary and grammar at the same time, but mostly your reading comprehension. Not that that doesn't happen elsewhere on this site; I've taken tests that had homophones and commonly confused words before. But if only they had had more than one such word in a row!
This test has 14 questions of varying difficulty, all involving homophones or homonyms that repeat at least once a sentence.
Initial reviewers of this test had mixed reactions ("fun", "not fun", "tough", and "tedious"), so let's consider this a beta version, and any feedback you can provide is greatly appreciated.