test $orig_invariant = $(git rev-parse invariant)
'
+test_expect_success 'setup submodule' '
+ rm -fr ?* .git &&
+ git init &&
+ test_commit file &&
+ mkdir submod &&
+ submodurl="$PWD/submod" &&
+ ( cd submod &&
+ git init &&
+ test_commit file-in-submod ) &&
+ git submodule add "$submodurl" &&
+ git commit -m "added submodule" &&
+ test_commit add-file &&
+ ( cd submod && test_commit add-in-submodule ) &&
+ git add submod &&
+ git commit -m "changed submodule" &&
+ git branch original HEAD
+'
+
+orig_head=`git show-ref --hash --head HEAD`
+
+test_expect_success 'rewrite submodule with another content' '
+ git filter-branch --tree-filter "test -d submod && {
+ rm -rf submod &&
+ git rm -rf --quiet submod &&
+ mkdir submod &&
+ : > submod/file
+ } || :" HEAD &&
+ test $orig_head != `git show-ref --hash --head HEAD`
+'
+
+test_expect_success 'replace submodule revision' '
+ git reset --hard original &&
+ git filter-branch -f --tree-filter \
+ "if git ls-files --error-unmatch -- submod > /dev/null 2>&1
+ then git update-index --cacheinfo 160000 0123456789012345678901234567890123456789 submod
+ fi" HEAD &&
+ test $orig_head != `git show-ref --hash --head HEAD`
+'
+
test_done