pkgs: tests: let
  formatValue = val:
    if (builtins.isList val || builtins.isAttrs val)
    then builtins.toJSON val
    else builtins.toString val;
  resultToString = {
    name,
    expected,
    result,
  }: ''
    ${name} failed: expected ${formatValue expected}, but got ${
      formatValue result
    }
  '';
  results = pkgs.lib.runTests (tests pkgs);
in
  if results != []
  then builtins.throw (builtins.concatStringsSep "\n" (map resultToString results))
  ## TODO: The derivation below is preferable but "nix flake check" hangs with it:
  ##       (it's preferable because "examples/many-failures" would then show all errors.)
  # pkgs.runCommand "nix-flake-tests-failure" { } ''
  #   cat <<EOF
  #   ${builtins.concatStringsSep "\n" (map resultToString results)}
  #   EOF
  #   exit 1
  # ''
  else pkgs.runCommand "nix-flake-tests-success" {} "echo > $out"