[impl-j][test] Add test coverage to CI

[at15]

• JUnit5 does not generate test to standard location
• seems no working converage tools JaCoCo [test] Use JUnit 5 #5 etc. Document code or automatically configure Jacoco with Junit 5 Gradle Plugin junit-team/junit5#1024
  • there is a blog https://vocabhunter.github.io/2017/10/17/migrating-to-junit-5.html
  • workaround based on PR's refer to that issue 8066a6d
• it seems our hits are all 1 .... while some should be more than one

The results of any tests run via the JUnit Platform Gradle plugin will not be included in the standard test report generated by Gradle; however, the test results can typically be aggregated by your CI server software. See the reportsDir property of the plugin
reportsDir file('build/test-results/junit-platform') // this is the default

• some code quality platforms (codecay, code beat) also support coverage report
  • didn't find the entrance in codebeat

Other code quality tools

• https://github.com/pmd/pmd
• https://github.com/spotbugs/spotbugs
• https://github.com/google/error-prone

[at15]

https://github.com/VocabHunter/VocabHunter/blob/a9c396e5796da72a6aeb2ce691bf034e4f8e06a2/build.gradle#L87-L105 it also provides example for checkstyle and pmd etc.

[at15]

following https://github.com/triplea-game/triplea/blob/master/build.gradle and it seems to work