RFR: 8336332: Rework tests to avoid unrelated stderr output [v12]

[Andy Goryachev]

On Thu, 18 Sep 2025 20:41:41 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:
> 
>   revert snapshot 1 test

I decided to remove Snapshot1Test from this PR: there is enough value added already, and there is more work needed to remove stderr output coming from CssParser anyway, so let's postpone it until the next test sprint.

follow up:
[JDK-8368023](https://bugs.openjdk.org/browse/JDK-8368023)
[TestBug] Rework tests to clean up stderr

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PR Comment: https://git.openjdk.org/jfx/pull/1897#issuecomment-3309659879