RFR: 8336332: Rework tests to avoid unrelated stderr output [v4]

[Andy Goryachev]

On Mon, 15 Sep 2025 19:25:37 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
>> - fixed ErrorLoggingUtiltity name
>
> Andy Goryachev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   moved utility

thanks for suggestions!  I'll revert back to DRAFT since there will be more structural changes, then we'll see if we can separate the two PRs or combine them.

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PR Comment: https://git.openjdk.org/jfx/pull/1897#issuecomment-3300257750