Adding missing test cases to exercise "React"

[patricknick]

When browsing through community solutions such as this one, I noticed that the current set of tests allow some shortcuts. Namely, there is two flaws that can be used:

• The tests only ever specify a single computed with an equality check and they only do that on computed that are known to be equal in the test case.
• The tests only specify callbacks that depend on the same input. This allowed solutions to implement a system that fires every callback, regardless which input changed.

The proposed test cases should prevent these shortcuts.

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