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

[Kevin Rushforth]

On Mon, 15 Sep 2025 19:25:37 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> This PR removes unrelated `stderr` output in the headful 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` (without failing the test).
>> 
>> ## How To
>> 
>> To redirect stderr and later check the exceptions, surround your code with
>> 
>> `ErrorLoggingUtility.suppressStderr()` and either `ErrorLoggingUtility.checkStderr()` or `ErrorLoggingUtility.checkAndRestoreStderr()`.
>> 
>> To simply undo redirection, without checking, call  `ErrorLoggingUtility.restoreStderr()`.
>> 
>> To add the check to all the tests in the file, one can call the above mentioned methods inside  `@BeforeEach` and `@AfterEach`.
>> 
>> ## Miscellaneous
>> 
>> For reviewers' convenience, the first commit contains the main change, the second fixes the misspelt name of the utility class, the rest are trivial.
>> 
>> ## Questions
>> 
>> - should we fail the current test with `Assertions.fail()` in case of a mismatch?
>
> Andy Goryachev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   moved utility

Two general comments before I start looking at the PR:

1. Since you are only addressing the `javafx.base` tests in this PR, please update the JBS title (and PR title) to reflect that.

2. In the description you wrote:

> This PR removes unrelated stderr output in the headful test logs

These are "headless" tests, not headful.

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PR Comment: https://git.openjdk.org/jfx/pull/1897#issuecomment-3299828328