diff --git a/docs/tickets/15.md b/docs/tickets/15.md
index 9a11629..b919e6e 100644
--- a/docs/tickets/15.md
+++ b/docs/tickets/15.md
@@ -119,7 +119,7 @@ With JS: dropdown/popover with format picker, async download.
 - [x] Implement wiki edit permissions in Namespace (`can_wiki_edit()`)
 - [x] Store revisions on edit (`node.wiki_edit()`)
 - [x] Revision history API endpoint
-- [ ] Diff endpoint (deferred — future work)
+- [x] Diff endpoint (`GET /api/v1/revisions/{id}/diff/{other_id}`)
 
 ### Phase 4: Auto-generated themes
 - [x] Per-namespace theme generation (light + dark)
diff --git a/remarkbox/tests/test_pandoc.py b/remarkbox/tests/test_pandoc.py
index 70aa369..c15da4e 100644
--- a/remarkbox/tests/test_pandoc.py
+++ b/remarkbox/tests/test_pandoc.py
@@ -1,8 +1,11 @@
 """Unit tests for remarkbox.lib.pandoc — pandoc subprocess wrapper."""
 
+import shutil
 import unittest
 import subprocess
 
+import pytest
+
 from remarkbox.lib.pandoc import (
     convert,
     node_tree_to_markdown,
@@ -63,6 +66,10 @@ class TestConvert(unittest.TestCase):
         self.assertIsInstance(result, bytes)
         self.assertGreater(len(result), 100)
 
+    @pytest.mark.skipif(
+        shutil.which("wkhtmltopdf") is None,
+        reason="wkhtmltopdf not installed",
+    )
     def test_markdown_to_pdf_returns_bytes(self):
         result = convert("# Test\n\nContent.", "markdown", "pdf", title="Test")
         self.assertIsInstance(result, bytes)
diff --git a/remarkbox/tests/test_undigg.py b/remarkbox/tests/test_undigg.py
index 0246774..2ef0da1 100644
--- a/remarkbox/tests/test_undigg.py
+++ b/remarkbox/tests/test_undigg.py
@@ -4,10 +4,13 @@ Tests the export, multi-syntax, wiki mode, and theme APIs end-to-end
 via webtest against the full Pyramid app.
 """
 
+import shutil
 import transaction
 import unittest
 import webtest
 
+import pytest
+
 from remarkbox.models import (
     Node,
     get_tm_session,
@@ -142,6 +145,10 @@ class TestExportThread(UndiggFunctionalTests):
         self.assertEqual(res.status_int, 200)
         self.assertIn(b"Test Thread", res.body)
 
+    @pytest.mark.skipif(
+        shutil.which("wkhtmltopdf") is None,
+        reason="wkhtmltopdf not installed",
+    )
     def test_export_thread_pdf(self):
         node_id = self._create_thread()
         res = self.testapp.get(