RFR: Initial section on testing [v2]

[Igor Ignatyev]

On Mon, 19 Oct 2020 21:34:53 GMT, Igor Ignatyev <iignatyev at openjdk.org> wrote:

>> Jesper Wilhelmsson has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Updates suggested by Phil and Igor
>
> Changes requested by iignatyev (no project role).

> > Besides the logistical information, I think it would be helpful to add
> > some conceptual information about JDK testing.
> 
> Yes, I think this is a good idea. There is some of this in /doc/hotspot-unit-tests.md but it's GTest specific and very
> HotSpot centric, so we should have something more generic and suitable for all. I have updated with a few sentences
> about this. Let me know if you think this needs to be expanded more or have any other suggestions.

[Writing jtreg tests](https://openjdk.java.net/jtreg/writetests.html) provides generic guidelines about _good_ jtreg
tests, but I'd say it's generic enough (as it should be as it's part of JTReg's documentation, not OpenJDK
documentation) and doesn't talk about things which are specific to OpenJDK, e.g. keywords, best practices, common
libraries, etc. [langtools guidelines]( https://openjdk.java.net/groups/compiler/tests.html), on the other hand,
provides langtools specific guidelines, some of them are adopted by other test suites, some not. I think it makes sense
for us to compose some OpenJDK-centric but generic enough guidelines and put them into either this guide or into
`/doc/jtreg-tests.md` and also have component/area-specific guidelines in `/doc/`.

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PR: https://git.openjdk.java.net/guide/pull/30