Add missing allergies tests

[BNAndras]

Inspired by https://forum.exercism.org/t/bug-expexted-and-actual-switched-allergies/52803, I flipped the expected and actual value order for the asserts. Then I remembered Assert.False`Assert.True` are available so I simplified the assertions. Then I realized not all tests were in fact present so I added those. The existing tests used multiple assertions per test so I simplified that so it's one assertion per test

[github-actions]

This PR touches files which potentially affect the outcome of the tests of an exercise. This will cause all students' solutions to affected exercises to be re-tested.

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[no important files changed]

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