RFR: 8285295: Need better testing for IdentityHashMap [v3]

[Stuart Marks]

On Wed, 4 May 2022 18:46:20 GMT, Stuart Marks <smarks at openjdk.org> wrote:

>> Basic but fairly comprehensive set of tests for `IdentityHashMap`. The patch in the bug report that breaks `IdentityHashMap` now causes several cases in this new test to fail. There's more that could be done, but the new tests cover most of the core functions of `IdentityHashMap`. Unfortunately it seems difficult to merge this with the existing, comprehensive Collections tests (e.g., MOAT.java) because those tests implicity rely on `equals()`-based contract instead of the special-purpose `==`-based contract used by `IdentityHashMap`.
>
> Stuart Marks has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Improve wording of comment.

I've added a few more assertions to cover `equals` of `entrySet` and `keySet` which I think were missing some cases. (Note that `values` returns a `Collection` which has no notion of equality.) I think this is ready now.

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PR: https://git.openjdk.java.net/jdk/pull/8354