core/pkgs/build-support/fetchurl/tests.nix

{ testers, fetchurl, jq, moreutils, ... }: {
  # Tests that we can send custom headers with spaces in them
  header = let headerValue = ''Test '" <- These are some quotes'';
  in testers.invalidateFetcherByDrvHash fetchurl {
    url = "https://httpbin.org/headers";
    sha256 = builtins.hashString "sha256" (headerValue + "\n");
    curlOptsList = [ "-H" "Hello: ${headerValue}" ];
    postFetch = ''
      ${jq}/bin/jq -r '.headers.Hello' $out | ${moreutils}/bin/sponge $out
    '';
  };
}