I see a lot of exceptions caused by RPC in the nightly build on Windows.
The most often is thrown by RPC on the namenode, saying
06/06/21 19:28:36 INFO ipc.Server: Server listener on port 7017: readAndProcess threw exception java.io.IOException: An existing connection was forcibly closed by the remote host. Count of bytes read: 0
java.io.IOException: An existing connection was forcibly closed by the remote host
at sun.nio.ch.SocketDispatcher.read0(Native Method)
I am not sure how serious that is, since the tests do not fail, and the name node does not crash.
Besides the RPC we should probably also check that the unit tests actually fail if they need to.