RFR: 8285295: Need better testing for IdentityHashMap [v4]

[Stuart Marks]

On Wed, 4 May 2022 19:16:14 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:
> 
>   Add some assertions for entrySet.equals and keySet.equals

> There should probably be something like [test/jdk/java/util/Collections/Wrappers.java](https://github.com/openjdk/jdk/blob/master/test/jdk/java/util/Collections/Wrappers.java)

Maybe. The intent of the test is fine, which is to ensure that a default method doesn't get added that breaks the invariants of the wrapper. One problem is that it tests only the default methods of `Collection` and not of the other collections interfaces. Another is that "override all default methods" isn't exactly the right criterion; instead, the criterion should be "override all default methods that would otherwise break this collection's invariants." It would be nice if such a test could be written, but as it stands I think that `Wrappers.java` test is too simplistic.

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