RFR: 8285295: Need better testing for IdentityHashMap [v2]

[Stuart Marks]

On Fri, 29 Apr 2022 03:00:40 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 two additional commits since the last revision:
> 
>  - Assertions over return values. Some refinement of equals() testing.
>  - Add comment about Map.Entry identity not guaranteed.

I've added checking of return values for I think everything that has a significant return value. I've elected to store the return value in a local variable and add a separate assert line. For example, instead of

    assertNull(map.put(newKey, newVal));

I've done

    Box r = map.put(newKey, newVal);
    assertNull(r);

The reason is that I think it separates the test setup/action from the test assertions. I tried it the first way, but it felt like the lack of this separation made things messy.

I've also added a couple more tests over `equals` and added more asserts over `equals` to the `keySet` and `entrySet` view sets. (Note, the `values` collection is just a `Collection` and thus doesn't have a defined notion of `equals`.) The testing of the view collections could probably be made more comprehensive, but I think what's here is a good start.

Please take a look.

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