this derivation will be built:
  /nix/store/cpqyicfj8fa3rlj0xpxacpi4zn6zj1l2-interpolate-conformance.drv
bld4: building cpqyicfj8fa3rlj0xpxacpi4zn6zj1l2-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected