Improve documentation on Parallel Test Execution

[bondolo]

I have some comments regarding configuring tests for parallel execution following reading: https://junit.org/junit5/docs/snapshot/user-guide/index.html#writing-tests-parallel-execution

Identifying all the relevant properties and the defaults for the properties in junit-platform.properties needs to be more obvious. They can be deduced from the narrative but perhaps should just be stated explicitly.

Also, a gentle approach for enabling parallelism should be suggested along with suggested mitigations when things don't work, as a sequence of steps that projects can evolve upon while still getting some parallelization benefit. An example for the Execution annotation would be useful as well. Non-parallel test execution could be considered a form of technical debt and a suggested approach for whittling away at that debt to make incremental progress towards as-parallel-as-practical execution. ie. help people figure out where they are now and what their next step should be along with necessary validation checks for each step.

Deliverables

• Add table of relevant configuration parameters
• Add example for using the @Execution annotation

[marcphilipp]

@bondolo Thanks for the feedback! Would you be interested in working on this via a more concrete outline here and then a PR?

[bondolo]

@marcphilipp I am definitely not an expert in this area. My suggestions above were based upon the concerns I struggled with in starting to enable parallelism in an existing project--a journey which is not yet completed. I would enthusiastically review any new material looking for ideas to advance our usage but, at this point, don't have much useful to contribute.

[MaratCrash]

@marcphilipp if its possible I can join to the issue and solve that.

[stoyanK7]

@bondolo Just made a table with the relevant properties, description, accepted values and default value. Is this what you envisioned?

[bondolo]

@stoyanK7 Yes, that is helpful!

[Kavisha4]

Hi @marcphilipp, interested to work on this, is this issue still open?

[marcphilipp]

@Kavisha4 Thanks for asking!

The table has been added in #2946 (comment).

I've added another deliverable to the issue description for which we'd accept a PR.

@bondolo If you have any other concrete suggestion, please let us know.