Surface the parsing errors of JUnit.xml on merge request
Since JUnit.xml is user-generated contents, GitLab could fail to parse if it's a corrupted xml.
In such case, we should surface the reason why test reports do not appear on merge requests/pipelne pages, and indicate that users should fix their script to correctly generate sane JUnit.xml.
I think we need to find a balance between
soft-failure(like a warning) and
hard-failure. I consider missing single test as a
soft-failure, so maybe we still allow this test case to be created but be
degenerated, but still be present on MR widget with relevant error?
I don't think that for the reason of single test we should fail the whole report.
The following discussion from gitlab-ce!20576 should be addressed: