ronn: add test for HTML reproducibility

pkgs/development/tools/ronn/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, lib, bundlerEnv, bundlerUpdateScript, makeWrapper, groff }:
+{ stdenv, lib, bundlerEnv, bundlerUpdateScript, makeWrapper, groff, callPackage }:
 
 stdenv.mkDerivation rec {
   pname = "ronn";
@@ -21,6 +21,8 @@ stdenv.mkDerivation rec {
 
   passthru.updateScript = bundlerUpdateScript "ronn";
 
+  passthru.tests.reproducible-html-manpage = callPackage ./test-reproducible-html.nix { };
+
   meta = with lib; {
     description = "markdown-based tool for building manpages";
     homepage = "https://rtomayko.github.io/ronn/";

pkgs/development/tools/ronn/test-reproducible-html.nix

@@ -0,0 +1,30 @@
+{ runCommand
+, diffutils
+, ronn
+}:
+runCommand "ronn-test-reproducible-html" { } ''
+  set -euo pipefail
+
+  cat > aprog.1.ronn << EOF
+  aprog
+  =====
+
+  ## AUTHORS
+
+  Vincent Haupert <veehaitch@users.noreply.github.com>
+  EOF
+
+  # We have to repeat the manpage generation a few times to be confident
+  # it is in fact reproducible.
+  for i in {1..20}; do
+    ${ronn}/bin/ronn --html --pipe aprog.1.ronn > aprog.1.html-1
+    ${ronn}/bin/ronn --html --pipe aprog.1.ronn > aprog.1.html-2
+
+    ${diffutils}/bin/diff -q aprog.1.html-1 aprog.1.html-2 \
+      || (printf 'The HTML manpage is not reproducible (round %d)' "$i" && exit 1)
+  done
+
+  echo 'The HTML manpage appears reproducible'
+
+  mkdir $out
+''