AFAIK, Its testsuite in parallel.
It looks like it's parallel in test case.
I think, you found this by checking logs for both passed tests and failed test in the same TestSuite right?
The report shows entire testsuite's logs for passed tests, and only particular testcase's logs for failed tests.
i.e. Failed Tests' logs also will be included in the passed tests' logs. Thats how you are seeing the collision. and thinking testcases runs in parallel.
Actually if you directly see the xml reports generated by sure-fire, there will not be any logs test-casewise for passed testcases.
And For the tests which fails with parallel tests enabled,
there can be 3 cases,
1. Port Binding issue, Ideally any port should not be hard coded. But some tests, expect DNs/NNs to restart in same ports, this could be the case.
2. Files written outside of test.build.data directory.
3. Waiting time for some events. In parallel tests, it needs to wait little more, since CPUs of build machines will be busy.
If any of tests fails with some other reasons, then might be some functional issue.