The failing tests are using MiniMRCluster and submit jobs. Jobs fail because containers' classpath does not contain the clover jar. If I make the leaf project to pick up non-clovered mr-client-app, at least AM works. But custom mapper, reducers, etc. defined in mr-client-jobclient will be instrumented and be part of the code running inside containers, so the containers should be able to locate the clover jar.
We have a record of these tests working with clover at least on June 24. So I went back and tried the old revision but it didn't work this time... I wonder how it ever worked.
MAPREDUCE-4082, it seems the classpath in mr-client-app contained the clover jar. The jira comments also shows clover being in the generated classpath. The now problematic clovered tests might have worked okay back then. Some tests were also being ignored.
MAPREDUCE-4141 that removed the hard dependency on clover. If these tests accidentally worked before, this might have stopped it.
Maybe running clovered test code in yarn containers does not make sense. They are separate processes launched by something other than the test framework. The clover instrumentation doesn't seem to be designed to naturally cover them. We could exclude some of test helper classes from instrumentation.