0 serial, 1 Design A, 2 Design B.
Test-only report of which parallel radix design ran: 0 serial, 1 A, 2 B.
The three answer identically by construction, so this is the only way a test of the Design A fallback can be non-vacuous -- A is reached only when B declines, and an assertion on the permutation cannot distinguish A, B and the serial loop.