Documented the RestartableJenkinsRule

[StefanSpieker]

Documented the RestartableJenkinsRule also created a very small example to showcase how it can be used.

[krisstern]

Thanks @StefanSpieker for the PR! I have made some minor edit suggestions.

[StefanSpieker]

Thanks for the suggestions, @krisstern !

[krisstern]

LGTM

[MarkEWaite]

Thanks! I like the documentation, but think that the heading should be changed from "Testing Durable Pipeline Steps" to "Testing Jenkins Restart", since the example is showing a test with a FreeStyleProject rather than a Pipeline step.

I don't think we should use RestartableJenkinsRule to test Pipeline steps because the workflow-durable-task-step plugin is no longer using RestartableJenkinsRule. It migrated from RestartableJenkinsRule to JenkinsSessionRule in this pull request:

• jenkinsci/workflow-durable-task-step-plugin#164

It added RealJenkinsRule based tests in these pull requests:

• jenkinsci/workflow-durable-task-step-plugin#323
• jenkinsci/workflow-durable-task-step-plugin#408

I think that documenting RestartableJenkinsRule is great. Thanks for doing it!

[StefanSpieker]

Thanks @MarkEWaite! You are right, since I just kept the existing headline, it does not really make sense. I will add some documentation for the JenkinsSessionRule in another PR. I'm trying to get the WIP of this testing done :)

[MarkEWaite]

Thanks!