new file mode 100755
--- /dev/null
+++ b/tests/test-bdiff
@@ -0,0 +1,42 @@
+#!/usr/bin/env python
+
+import sys
+from mercurial import bdiff, mpatch
+
+def test1(a, b):
+    d = bdiff.bdiff(a, b)
+    c = a
+    if d:
+        c = mpatch.patches(a, [d])
+    if c != b:
+        print "***", `a`, `b`
+        print "bad:"
+        print `c`[:200]
+        print `d`
+
+def test(a, b):
+    print "***", `a`, `b`
+    test1(a, b)
+    test1(b, a)
+
+test("a\nc\n\n\n\n", "a\nb\n\n\n")
+test("a\nb\nc\n", "a\nc\n")
+test("", "")
+test("a\nb\nc", "a\nb\nc")
+test("a\nb\nc\nd\n", "a\nd\n")
+test("a\nb\nc\nd\n", "a\nc\ne\n")
+test("a\nb\nc\n", "a\nc\n")
+test("a\n", "c\na\nb\n")
+test("a\n", "")
+test("a\n", "b\nc\n")
+test("a\n", "c\na\n")
+test("", "adjfkjdjksdhfksj")
+test("", "ab")
+test("", "abc")
+test("a", "a")
+test("ab", "ab")
+test("abc", "abc")
+test("a\n", "a\n")
+test("a\nb", "a\nb")
+
+print "done"