The refactored oeqa framework provides a standard way to define decorators so implement OETimeout decorator, this will send a SIGALARM when some time expires to the OETestCase.
This has been implemented in contrib branch mariano/oeqa_improvements: http://git.yoctoproject.org/cgit/cgit.cgi/poky-contrib/log/?h=mariano/oeqa_improvements
Patch sent for review: https://patchwork.openembedded.org/series/4272/#
This has been solved in commit: http://cgit.openembedded.org/openembedded-core/commit/?id=1bf66a370361912e9950d7ff45e382c93622a169