this derivation will be built:
  /nix/store/wc2hl8i8xqrj6qca32ivblqr1i29aaxj-interpolate-conformance.drv
bld4: building wc2hl8i8xqrj6qca32ivblqr1i29aaxj-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected