python3Packages.pywal: use $TMPDIR in tests

darwin hydra can fail to access /tmp

pkgs/development/python-modules/pywal/default.nix

@@ -9,24 +9,29 @@ buildPythonPackage rec {
     sha256 = "1drha9kshidw908k7h3gd9ws2bl64ms7bjcsa83pwb3hqa9bkspg";
   };
 
-  preCheck = ''
-    mkdir tmp
-    HOME=$PWD/tmp
-  '';
-
   patches = [
     ./convert.patch
     ./feh.patch
   ];
 
-  # Invalid syntax
-  disabled = !isPy3k;
-
   postPatch = ''
     substituteInPlace pywal/backends/wal.py --subst-var-by convert "${imagemagick}/bin/convert"
     substituteInPlace pywal/wallpaper.py --subst-var-by feh "${feh}/bin/feh"
   '';
 
+  # Invalid syntax
+  disabled = !isPy3k;
+
+  preCheck = ''
+    mkdir tmp
+    HOME=$PWD/tmp
+
+    for f in tests/test_export.py tests/test_util.py ; do
+      substituteInPlace "$f" \
+        --replace '/tmp/' "$TMPDIR/"
+    done
+  '';
+
   meta = with lib; {
     description = "Generate and change colorschemes on the fly. A 'wal' rewrite in Python 3";
     homepage = "https://github.com/dylanaraps/pywal";