allergies: add missing tests from problem spec

[kahgoh]

While working on the allergies exercise on the Elm track, I noticed there were a number of cases from the problem specification. I used the generate_practice_exercise.sh script to help get the missing tests.

[ceddlyburge]

Hi Kah, thanks for this PR, it looks like you have added a lot of tests, and made things consistent with the other tracks.
Could you take a look at the build errors? I had a very brief look and I think you need to run elm-format.
Cheers, Cedd

[jiegillet]

Cool, thanks!
Can you also run ./bin/configlet sync --update --tests --exercise allergies to update the tests.toml (it might not even exist yet, I'm not sure)

[kahgoh]

Cool, thanks! Can you also run ./bin/configlet sync --update --tests --exercise allergies to update the tests.toml (it might not even exist yet, I'm not sure)

Confirming, I've ran this - it didn't produce any diff according to Git. There was already a test.toml that listed all the tests from the problem spec.