nix: introduce single-page tests

default.nix

@@ -8,6 +8,9 @@
   # When doing development you may want to shut this off to obtain the
   # output file that you need to check in.
 , doOutputDiff ? true
+  # Attempts to render every page individually to make sure the dependencies
+  # are set correctly.
+, doPageChecks ? true
 }:
 
 let
@@ -204,15 +207,37 @@ in
 stdenv.mkDerivation {
   name = "codex32${shortId}";
 
-  buildInputs = if doPdfGeneration then [ ghostscript ] else [ ];
+  buildInputs = [ ghostscript ];
 
   phases = [ "buildPhase" ];
   buildPhase = ''
     set -e
 
+    ghostscriptTest() {
+      echo "Ghostscript testing $1"
+      local output;
+      if ! output="$(gs -dNOPAUSE -dNODISPLAY "$1" < /dev/null 2>&1)"; then
+        echo "Failed to run ghostscript on $1"
+        echo "$output"
+        exit 1
+      fi
+    }
+  '' + lib.optionalString doPageChecks toString (
+    map
+      (page:
+        let
+          pageFile = renderBooklet
+            {
+              name = "test-single-page.ps";
+              pages = [ page ];
+            };
+        in "ghostscriptTest ${pageFile}\n")
+        fullBooklet.pages) + ''
+    FULL_BW="${renderBooklet fullBooklet}"
+    ghostscriptTest "$FULL_BW"
     mkdir "$out"
     cd "$out"
-    cp ${renderBooklet fullBooklet} SSS32.ps
+    cp "$FULL_BW" SSS32.ps
 
     ${lib.optionalString doOutputDiff "diff -C 5 ${src}/SSS32.ps SSS32.ps"}
     sed -i 's/(revision \(.*\))/(revision \1${shortId})/' ./SSS32.ps