anchor.diff:  
       "rhel-8" = {
         image = import <nix/fetchurl.nix> {
  -        url = https://app.vagrantup.com/generic/boxes/rhel8/versions/4.1.12/providers/libvirt.box;
  +        url = "https://app.vagrantup.com/generic/boxes/rhel8/versions/4.1.12/providers/libvirt.box";
           hash = "sha256-zFOPjSputy1dPgrQRixBXmlyN88cAKjJ21VvjSWUCUY=";
         };
         rootDisk = "box.img";
  
positive.code: 
      "fedora-36" = {
        image = import <nix/fetchurl.nix> {
          url = https://app.vagrantup.com/generic/boxes/fedora36/versions/4.1.12/providers/libvirt.box;
          hash = "sha256-rxPgnDnFkTDwvdqn2CV3ZUo3re9AdPtSZ9SvOHNvaks=";
        };
        rootDisk = "box.img";
  
negative.code: 
      "ubuntu-22-04" = {
        image = import <nix/fetchurl.nix> {
          url = "https://app.vagrantup.com/generic/boxes/ubuntu2204/versions/4.1.12/providers/libvirt.box";
          hash = "sha256-HNll0Qikw/xGIcogni5lz01vUv+R3o8xowP2EtqjuUQ=";
        };
        rootDisk = "box.img";
  