RFR: 8289511: Improve test coverage for XPath Axes: child [v3]

[Joe Wang]

On Thu, 14 Jul 2022 20:52:18 GMT, Bill Huang <duke at openjdk.org> wrote:

>> This is a subtask of [JDK-8286091](https://bugs.openjdk.org/browse/JDK-8286091) which is aiming to improve XPath expression test coverage. The goal of this subtask is validating the XPath child axis specifier in various ways.
>
> Bill Huang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Renamed XPahtExpChildTest.java and moved NPE test cases from invalid test case to zero children test case.

Sounds good. @bwhuang-us Bill, could you edit the title to match the JBS. I've changed the synopsis for all subtasks.
nvm, I changed the subtask to match the PR.

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PR: https://git.openjdk.org/jdk/pull/9484