this derivation will be built:
  /nix/store/jk2440cg0hqnd79sv0ngip6wq52aj9lr-interpolate-conformance.drv
bld4: building jk2440cg0hqnd79sv0ngip6wq52aj9lr-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected