RocksDBStateBackendTest#testCancelRunningSnapshot sometimes fails

testCancelRunningSnapshot[1](org.apache.flink.contrib.streaming.state.RocksDBStateBackendTest)  Time elapsed: 0.166 sec  <<< FAILURE!
java.lang.AssertionError: null
  at org.junit.Assert.fail(Assert.java:86)
  at org.junit.Assert.assertTrue(Assert.java:41)
  at org.junit.Assert.assertTrue(Assert.java:52)
  at org.apache.flink.contrib.streaming.state.RocksDBStateBackendTest.testCancelRunningSnapshot(RocksDBStateBackendTest.java:313)


Results :

Failed tests:
  RocksDBStateBackendTest.testCancelRunningSnapshot:313 null

    assertTrue(testStreamFactory.getLastCreatedStream().isClosed());