Test instability in OneInputStreamTaskTest#testWatermarkMetrics

Tests run: 9, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 2.86 sec <<< FAILURE! - in org.apache.flink.streaming.runtime.tasks.OneInputStreamTaskTest
testWatermarkMetrics(org.apache.flink.streaming.runtime.tasks.OneInputStreamTaskTest)  Time elapsed: 1.141 sec  <<< FAILURE!
java.lang.AssertionError: expected:<1> but was:<-9223372036854775808>
	at org.junit.Assert.fail(Assert.java:88)
	at org.junit.Assert.failNotEquals(Assert.java:834)
	at org.junit.Assert.assertEquals(Assert.java:645)
	at org.junit.Assert.assertEquals(Assert.java:631)
	at org.apache.flink.streaming.runtime.tasks.OneInputStreamTaskTest.testWatermarkMetrics(OneInputStreamTaskTest.java:731)