this derivation will be built:
  /nix/store/r12vb5fx6l713as6y8r1vkw8wdqln5hh-interpolate-conformance.drv
bld4: building r12vb5fx6l713as6y8r1vkw8wdqln5hh-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected