--- a/tests/test-git-interop.t	Mon Jun 01 11:12:25 2020 -0400
+++ b/tests/test-git-interop.t	Wed Jun 03 11:28:57 2020 -0400
@@ -253,3 +253,11 @@
 
 This coveres changelog.findmissing()
   $ hg merge --preview 3d9be8deba43
+
+This covers manifest.diff()
+  $ hg diff -c 3d9be8deba43
+  diff -r c5864c9d16fb -r 3d9be8deba43 beta
+  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/beta	Mon Jan 01 00:00:11 2007 +0000
+  @@ -0,0 +1,1 @@
+  +beta