RepositoryTest#validateAllFeatures is flickering

java.lang.AssertionError
	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.xwiki.test.ui.repository.RepositoryTest.importExtension(RepositoryTest.java:377)
	at org.xwiki.test.ui.repository.RepositoryTest.validateAllFeatures(RepositoryTest.java:109)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        ...