The final production testing is done by skilled technicians who have the ability to test two at a time, in tandem. They’ve got some test hardware that I’m jealous of (fast-removal memory modules, CPU heatsinks that don’t need full attachment, PCI and PCI Express logic testers, etc.) and can have a mainboard fully functionally tested in a matter of minutes.
I believed that building a motherboard was done all by machines, but was I wrong. This is a fantastic article if you care at all to see how your motherboards are made. Check it out at Hexus.