Thanks everyone for your comments and feedback on the QA testing process. I have updated the section on running tests in the QA testing guide so that it now says:
Select a test from the list. If you wish, you can click the 'Assign to me' button, so that nobody else chooses the same test to run. (If you then find you are unable to run the test, you can assign the issue to 'Nobody'.)
Please note though, that when a failed test is reset (after a bug is fixed), the assignee is automatically set to 'Nobody', since although it is a great help for the original tester to re-run the test, we don't want to assume that they have the time to do so.
Regarding having more test materials (activities, groups, data etc) on the QA testing site, we hope to improve the site in time for the next QA testing cycle.
As mentioned previously, so far over a hundred QA tests have been automated as part of the Behat project in Moodle and are now run automatically every week. The plan is to automate as many of the straightforward QA tests as possible and remove them from the testing cycle, then add more exploratory QA tests covering new features and improvements in the upcoming version.
Having the help if the Moodle community in QA testing is wonderful and much appreciated.