RFR: 8296284: Update CONTRIBUTING guidelines to state that JUnit 5 is used for tests [v2]

[Andy Goryachev]

On Wed, 18 Jun 2025 12:15:14 GMT, Marius Hanl <mhanl at openjdk.org> wrote:

>> As written in the ticket, we might want to clarify that we use `JUnit5` for testing in the `CONTRIBUTING` guidelines.
>> 
>> This is a first idea of how we could document this and also link to the JUnit page in case contributors are not familiar with the framework (or `JUnit5` in particular). 
>> 
>> Feedback welcome!
>
> Marius Hanl has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Move JUnit5 reference to 'Test your changes'

Marked as reviewed by angorya (Reviewer).

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PR Review: https://git.openjdk.org/jfx/pull/1828#pullrequestreview-2939546422