RFR: 8244297: memory leak test utility

[Kevin Rushforth]

On Sun, 3 May 2020 21:39:41 GMT, Florian Kirmaier <fkirmaier at openjdk.org> wrote:

> It's based on the discussion of my previous PR: https://github.com/openjdk/jfx/pull/71
> 
> I Added test utility class copied from JMemoryBuddy and used it to simplify 4 of the existing unit tests.
> 
> It's a direct copy of my project [JMemoryBuddy](https://github.com/Sandec/JMemoryBuddy) without any changes.
> I'm also using it in most of the projects I'm involved with and in my experience, the tests with this Library are very
> stable. I can't remember wrong test results. Sometimes the memory behaviour of some libraries itself is not stable but
> the tests with JMemoryBuddy are basically always correct.

I'll put this on my queue to review and test it. I left some high-level comments below.

modules/javafx.base/src/test/java/de/sandec/jmemorybuddy/JMemoryBuddy.java line 1:

> 1: package de.sandec.jmemorybuddy;
> 2:

This file needs a standard Oracle copyright header, which you can copy from any of the other test files.

Also, this utility class should be moved into a package matching the pattern we already use for our tests. Something
like `test.util.memory`?

modules/javafx.base/src/test/java/de/sandec/jmemorybuddy/JMemoryBuddy.java line 145:

> 144:
> 145:     public static void createHeapDump() {
> 146:         try {

I don't think we want automatic creation of heap dumps by our unit test suite. That would need a larger discussion. I
recommend to either comment this out, or else to qualify it with a system property that could be passed in via a
`gradle` property (e.g., as is done for `UNSTABLE_TEST`), with a default of `false`.

modules/javafx.base/src/test/java/de/sandec/jmemorybuddy/JMemoryBuddy.java line 15:

> 14:
> 15: public class JMemoryBuddy {
> 16:

Since this is a utility intended to be used by various tests, it would be very helpful to add some documentation about
how to use it.

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PR: https://git.openjdk.java.net/jfx/pull/204