test_buildhistory_does_not_change_signatures is running 6 times in oe-selftest build step. Because this tests is located in buildhistory/BuildhistoryBase which is inherited by other classes it runs multiple times. This test should be removed from BuildhistoryBase base class.
Patch sent to ML: http://lists.openembedded.org/pipermail/openembedded-core/2016-January/114751.html Moved test_buildhistory_does_not_change_signatures from buildhistory/BuildhistoryBase to buildoptions/BuildhistoryTests.
Fixed in oe-core 975e67e28ccba5dcb0fced43c1f9e7da183dc201.