I have seen this failing on Travis with Open JDK 7. It seems it passes on different runs. I haven't checked yet, but it's probably related to execution being slower.
testMonitoredCounterGroup(org.apache.flume.source.TestExecSource) Time elapsed: 3997 sec <<< FAILURE!
org.junit.ComparisonFailure: Expected Value: 5 expected:<> but was:<>