I find that with some harder words, I lose hearts because I can't remember how to spell them. Especially new words are hard to spell. A spelling test section may be an idea for commonly misspelled words.
I really like Quizlet for spelling.
It is a flashcard site, but they have a 'spelling' option.
You have to make the flashcards yourself (or search Duolingo French to see if anyone else has made some). When you pick the spelling option, you are given the definition of the word in English and you get to hear it in your target language (French). You have to spell it correctly twice in a row before it assumes you know the spelling. It has helped me a lot.