As a user, I can filter Test Plans in a list of Tests using a JQL function

The jql function testTestPlan() should be improved in order to support either a specific Test issue key or a saved_filter_containing_test_issues.

If a saved filter is provided, then all Test Plans linked to each one of the Tests will be returned. Note that this doesn't mean that the Tests have to be part of all of those Test Plans.

ex: 

issuetype = 'Test Plan' and key in testTestPlan('my_list_of_test_issues')