Abstract: A method for testing a processor subassembly includes providing a computer system comprising subassemblies. Each subassembly includes processors having internal communication paths and ports that provide external communication paths to other subassemblies via a midplane circuit board. For each subassembly, a first port is connected to a second port via the midplane circuit board, thereby re-routing external communication paths back to the subassembly instead of to other subassemblies and allowing communication between the processors through external paths. Each subassembly can be tested one at a time.