find common prefix and suffix of two strings

kitty_tests/diff.py

@@ -0,0 +1,23 @@
+#!/usr/bin/env python
+# vim:fileencoding=utf-8
+# License: GPL v3 Copyright: 2018, Kovid Goyal <kovid at kovidgoyal.net>
+
+
+from . import BaseTest
+
+
+class TestDiff(BaseTest):
+
+    def test_changed_center(self):
+        from kittens.diff.diff_speedup import changed_center
+        for left, right, prefix, suffix in [
+                ('abc', 'def', '', ''),
+                ('', 'def', '', ''),
+                ('abc', '', '', ''),
+                ('abc', 'abc', 'abc', ''),
+                ('abc', 'abcdef', 'abc', ''),
+                ('aa111bb', 'aa2bb', 'aa', 'bb'),
+        ]:
+            pc, sc = changed_center(left, right)
+            for src in (left, right):
+                self.assertEqual((prefix, suffix), (src[:pc], src[-sc:] if sc else ''))