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The idea of a fixture isn't new. It's an idea from the hardware world, the manufacture of CHIPs. When a new chip is created it needs to be analysed and tested. In order to do this the designers would create a special PCB onto which the new chip would be mounted. The PCB would have several connectors from it, these connectors would be connected to test and analysis devices. The PCB is known as a fixture. It's basically an adapter that allows massages to be translated to and from the chip to its test environment.
Google search "cpu test fixture" for images of this principle.