I've converted a freestyle job that used the DynamicAxis Plugin to execute multiple functional tests at the same time.
I ported using this approach - https://github.com/jenkinsci/pipeline-plugin/blob/master/TUTORIAL.md#creating-multiple-threads and this https://support.cloudbees.com/hc/en-us/articles/115000088431-Create-a-Matrix-like-flow-with-Pipeline
The job works well. The part I am having a problem with is tying a published HTML report with a given test run. In the freestyle / matrix job, you drill into each test run and see the 'HTML Report' link in the left nav that was created from the specific test run.
Since the parallel pipeline approach does not provide a link to the 'Configuration' run like the freestyle / matrix job (see screenshot), I'm not sure how to get a similar UX:
I suppose I could use the Summary Display Plugin and attempt to manage the HTML Report run from each test job.
I'm only executing publishHTML when an error occurs and am giving the HTML Report link in the left nav a unique value (including the test name) so that each test failure has a link to the HTML artifacts.