this derivation will be built:
  /nix/store/80lkjx61xvcc91c2mxbpajfsrna6hcgh-interpolate-conformance.drv
bld3: building 80lkjx61xvcc91c2mxbpajfsrna6hcgh-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected