When diffstat is available, dulwich.patch.write_commit_patch() adds the

diffstat followed by a "\n", just before the contents and version info.
The assertion in test_simple() assumes that this is always the case, and
breaks when the diffstat is absent.

dulwich/tests/test_patch.py

@@ -54,9 +54,8 @@ class WriteCommitPatchTests(TestCase):
             "\n",
             "---\n"], lines[3:8])
         self.assertEquals([
-            "\n",
             "CONTENTS-- \n",
-            "custom\n"], lines[-3:])
+            "custom\n"], lines[-2:])
         if len(lines) >= 12:
             # diffstat may not be present
             self.assertEquals(lines[8], " 0 files changed\n")