jgraham gave a good summary here: https://bugzilla.mozilla.org/show_bug.cgi?id=1042921#c2 I've been hacking around this when converting XPCShell and CPP tests as well. Let's agree on invariants for users of the logging library and enforce them in mozlog.structured. bug 933885 and bug 991866 seem like good background for this sort of issue.

Standard library logging does this: http://hg.python.org/cpython/file/ee879c0ffa11/Lib/logging/__init__.py#l859 I don't assume this does the right thing in every case, but may have enough users that it will do something reasonable for common uses.

The solution to bug 1042921 addressed this.