Use junit-pioneer to simplify polluted tests

[abelsromero]

Kind of change

• [ ] Bug fix
• [x] New non-breaking feature
• [ ] New breaking feature
• [ ] Documentation update
• [ ] Build improvement

Description

What is the goal of this pull request?

Simplify Gradle build and fix some IDE integration issues. See #1193 for details.

How does it achieve that?

• Add junit-pioneer to inject environment variables into tests. This allows removing custom Gradle task pollutedTest and running them normally.
• Refactor WhenAnAsciidoctorClassIsInstantiatedInAnEnvironmentWithGemPath as a parametrized tests.
• Add missing cases for Asciidoctor Factory in WhenAnAsciidoctorClassIsInstantiatedInAnEnvironmentWithGemPath.

Are there any alternative ways to implement this?

Discussed in #1193.

Are there any implications of this pull request? Anything a user must know?

No, if anything, it should be easier for contributors now.

Issue

If this PR fixes an open issue, please add a line of the form:

Fixes #1193

Release notes

Please add a corresponding entry to the file CHANGELOG.adoc

[abelsromero]

I added the missing Asciidoctor Factory cases and asserted them based on the returned values. @robertpanzer cpould you please double-check nothing is wrong?

[abelsromero]

"drafting" while I look into the test that failed 😞

[abelsromero]

I had to apply a workaround for Windows builds only to set --add-opens to the test task. Not elegant but allows us to keep the code and overall configuration simpler than before.

[robertpanzer]

Thanks! 👍