RFR: 8336332: Rework tests to avoid unrelated stderr output [v7]

[Andy Goryachev]

On Thu, 18 Sep 2025 15:26:27 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> This PR removes unrelated `stderr` output in the headless test logs by redirecting it to an in-memory buffer.  Exceptions found in the buffer can be checked against the expected list.
>> 
>> In the case when any mismatch is detected, whether the type or the number of exceptions of particular type, the accumulated buffer gets dumped to `stderr` and the test fails.
>> 
>> ## How To
>> 
>> To redirect stderr and later check the exceptions, surround your code with
>> 
>> `OutputRedirect.suppressStderr()` and either `OutputRedirect.checkStderr()` or `OutputRedirect.checkAndRestoreStderr()` (ideally, in the `finally` block).
>> 
>> To simply undo redirection, without checking, call  `OutputRedirect.restoreStderr()`.
>> 
>> To add the check to all the tests in the file, one can call the above mentioned methods inside  `@BeforeEach` and `@AfterEach`.
>> 
>> ## Changes
>> 
>> - added `OutputRedirect` facility
>> 
>> ## Miscellaneous
>> 
>> `ErrorLoggingUtiltity` name will be fixed in a followup https://bugs.openjdk.org/browse/JDK-8367995
>
> Andy Goryachev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   cleanup

regex: I can try commenting what each part means

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PR Comment: https://git.openjdk.org/jfx/pull/1897#issuecomment-3308340639