diff --git a/tests/_support_data/gen-data.sh b/tests/_support_data/gen-data.sh
index f2c5189..457157c 100755
--- a/tests/_support_data/gen-data.sh
+++ b/tests/_support_data/gen-data.sh
@@ -15,3 +15,13 @@ mkdir -p tool_repos/uninitialized.git
 git init --bare tool_repos/initialized.git
 git init tool_repos/non-bare-init
 
+echo "Preparing submodules for tests.."
+for repo in test-repo-*
+do
+	echo ">> $repo"
+	cd $repo
+	for i in $(git for-each-ref --format="%(refname:short)" --no-merged=origin/HEAD refs/remotes/origin); do git switch --track $i; done
+	cd ..
+done
+# recover submodules to initial state (branches will remain)
+git submodule update --init