Add missing test file.
diff --git a/src/testdir/test_ex_undo.vim b/src/testdir/test_ex_undo.vim
new file mode 100644
index 0000000..44feb36
--- /dev/null
+++ b/src/testdir/test_ex_undo.vim
@@ -0,0 +1,19 @@
+" Tests for :undo
+
+func Test_ex_undo()
+ new ex-undo
+ setlocal ul=10
+ exe "normal ione\n\<Esc>"
+ setlocal ul=10
+ exe "normal itwo\n\<Esc>"
+ setlocal ul=10
+ exe "normal ithree\n\<Esc>"
+ call assert_equal(4, line('$'))
+ undo
+ call assert_equal(3, line('$'))
+ undo 1
+ call assert_equal(2, line('$'))
+ undo 0
+ call assert_equal(1, line('$'))
+ quit!
+endfunc