this derivation will be built:
  /nix/store/n8i469v6vqijyh5lj53ff64r27pc08kh-interpolate-conformance.drv
bld4: building n8i469v6vqijyh5lj53ff64r27pc08kh-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected