test_cmp expected actual
'
+test_expect_success 'setup nested submodule' '
+ git submodule add -f ./sm2 &&
+ git commit -a -m "add sm2" &&
+ git -C sm2 submodule add ../sm2 nested &&
+ git -C sm2 commit -a -m "nested sub"
+'
+
+test_expect_success 'move nested submodule HEAD' '
+ echo "nested content" >sm2/nested/file &&
+ git -C sm2/nested add file &&
+ git -C sm2/nested commit --allow-empty -m "new HEAD"
+'
+
+test_expect_success 'diff --submodule=diff with moved nested submodule HEAD' '
+ cat >expected <<-EOF &&
+ Submodule nested a5a65c9..b55928c:
+ diff --git a/nested/file b/nested/file
+ new file mode 100644
+ index 0000000..ca281f5
+ --- /dev/null
+ +++ b/nested/file
+ @@ -0,0 +1 @@
+ +nested content
+ EOF
+ git -C sm2 diff --submodule=diff >actual 2>err &&
+ test_must_be_empty err &&
+ test_cmp expected actual
+'
+
test_done