this derivation will be built:
  /nix/store/lijkx39nywpvms5yjhff6v837c91zsf2-interpolate-conformance.drv
bld4: building lijkx39nywpvms5yjhff6v837c91zsf2-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected