When I was studying for my CELPIP exam I got material from them. Unfortunately, I can not put the PDF to the public because it has a watermark with my personal email. But I can put you here what it says.
CELPIP's twentieth-third error as they state:
Homonyms are words that sound the same but have different spellings and meanings. An example is "none" (zero) and "nun" (a holy woman). These two words are pronounced exactly the same, but as you can see, their meaning and spelling are different.
Malapropisms are words that are frequently mistaken for other words because they look and sound somewhat similar. Malapropisms often result in nonsensical and humorous errors. An example is, "My aunt is in a comma." A "comma" is a punctuation symbol; this person means to say that her aunt is in a "coma"(is unconscious).
Mistakes with homonyms and malapropisms are common in the CELPIP Writing Test. Sometimes this problem occurs because of overreliance on the Spell Check feature. Remember, the computer can only determine if a word is incorrectly spelled. It cannot tell you if you've used the wrong word. Sometimes, this word choice error is the result of a problem with spelling or typing. Test takers either don't know the correct spelling of a word and guess incorrectly, or they type the wrong word. Eighter way, an improper word is used.
The use of improper word forms, as they can easily be confused: