docs: describe pre-rebase hook

diff --git a/t/t4027-diff-submodule.sh b/t/t4027-diff-submodule.sh
index 1fd3fb74d763026d4e20a38fe9d2ed48dda74fed..ba6679c6e4032bb12e4206226f95770946ece8cc 100755 (executable)
--- a/t/t4027-diff-submodule.sh
+++ b/t/t4027-diff-submodule.sh
@@ -50,4 +50,11 @@ test_expect_success 'git diff-files --raw' '
        test_cmp expect actual.files
 '
 
+test_expect_success 'git diff (empty submodule dir)' '
+       : >empty &&
+       rm -rf sub/* sub/.git &&
+       git diff > actual.empty &&
+       test_cmp empty actual.empty
+'
+
 test_done