RFR: JDK-8296240: Augment discussion of test tiers in doc/testing.md [v2]

[Joe Darcy]

On Fri, 27 Oct 2023 00:51:26 GMT, Leonid Mesnik <lmesnik at openjdk.org> wrote:

> It is not clear why the time limit is 10 seconds. There are hundreds of tests in current tier1 that currently take longer than 10 seconds.

I haven't looked at the exact running time recently, but I'd expect there are thousands of tests that run in a fraction of a second.

The 10 second guideline is a guideline rather than a strict requirement, but I would encourage tests that run that long or longer to be refactored or split into pieces (or for a very long-running test, moved to a higher numbered tier).

The tier 1 tests are run all the time so there is value in keeping the aggregate running time of the tier 1 tests as a whole down and if the tests are (nearly) all short-running the test suite is more parallelizable and there are fewer Amdahl's law hazards.

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PR Comment: https://git.openjdk.org/jdk/pull/16384#issuecomment-1782172053