this derivation will be built:
  /nix/store/ikjl64dy8z9yypa4574lvbn8q9igj6vc-interpolate-conformance.drv
bld4: building ikjl64dy8z9yypa4574lvbn8q9igj6vc-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected