You're using Ubuntu, too - that's great (and safes me a lot of money, and frustration :-]) I'll give Netbeans one more try, the Stapler plugin makes me curious.
First, here is the CpsScriptTest failure I get:
Tests run: 3, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 4.815 sec <<< FAILURE! - in org.jenkinsci.plugins.workflow.cps.CpsScriptTest
evaluateShallBeCpsTransformed(org.jenkinsci.plugins.workflow.cps.CpsScriptTest) Time elapsed: 2.715 sec <<< FAILURE!
org.codehaus.groovy.runtime.powerassert.PowerAssertionError: assert future != null
CpsScriptTest.evaluateShallBeCpsTransformed:74 assert future != null
Tests run: 21, Failures: 1, Errors: 0, Skipped: 0
The test code in tag 'workflow-1.1' was different, but it failed, too.
Second, you may have guessed that I'm a Jenkins-dev newbie (comming from the world of embedded control). I assumed that I better don't issue any pull-request before I know that my code doesn't break tests (which I can't when I switch off tests . Assumptions are often wrong, but I read all the docs on development carefully, and it they only told me to run 'mvn clean install', there is no word about skipping the tests. Of course, you must assume a certain 'dev proficiency', but sometimes such things make the learning curve steep.
Third, try adding a directory ~/.jenkins without write access, and run 'mvn clean install'. On my machine this makes (many) tests fail. On the other hand, if that folder doesn't exist, it's there after the test are done.
This is what I find there:
thomas@thomas-W500:~$ ls .jenkins/
thomas@thomas-W500:~$ ls .jenkins/cache/
thomas@thomas-W500:~$ ls .jenkins/cache/jars/
04 1A 2C 3A 4B 50 53 63 68 76 86 94 A7 D2 DB F5
09 1F 37 43 4F 52 61 65 69 78 8D 9B C2 D5 F2 FE
thomas@thomas-W500:~$ ls .jenkins/cache/jars/04
Maybe that's because I run 'mvn install' from the workflow-plugin root, and not from 'aggregator', but in my opinion that's not obvious.
It would also have been helpful to know, where I should run 'mvn hpi:run' (maybe it's obvious, but the workflow plugin is a 'bit' more complex than most examples , and I have still to figure out how to do this with netbeans).
Of course, most of this isn't a problem of the workflow-plugin, but every bit of information helps.