this derivation will be built:
  /nix/store/na9gdx7ycxlvnabbciapfk7p7lchi9lp-interpolate-conformance.drv
bld4: building na9gdx7ycxlvnabbciapfk7p7lchi9lp-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected