TestCapacitySchedulerSurgicalPreemption sometimes fails

testSimpleSurgicalPreemption(org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.TestCapacitySchedulerSurgicalPreemption)  Time elapsed: 14.671 sec  <<< FAILURE!
java.lang.AssertionError: null
	at org.junit.Assert.fail(Assert.java:86)
	at org.junit.Assert.fail(Assert.java:95)
	at org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.CapacitySchedulerPreemptionTestBase.waitNumberOfLiveContainersFromApp(CapacitySchedulerPreemptionTestBase.java:110)
	at org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.TestCapacitySchedulerSurgicalPreemption.testSimpleSurgicalPreemption(TestCapacitySchedulerSurgicalPreemption.java:143)

testSurgicalPreemptionWithAvailableResource(org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.TestCapacitySchedulerSurgicalPreemption)  Time elapsed: 9.503 sec  <<< FAILURE!
java.lang.AssertionError: expected:<3> but was:<2>
	at org.junit.Assert.fail(Assert.java:88)
	at org.junit.Assert.failNotEquals(Assert.java:743)
	at org.junit.Assert.assertEquals(Assert.java:118)
	at org.junit.Assert.assertEquals(Assert.java:555)
	at org.junit.Assert.assertEquals(Assert.java:542)
	at org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.TestCapacitySchedulerSurgicalPreemption.testSurgicalPreemptionWithAvailableResource(TestCapacitySchedulerSurgicalPreemption.java:220)