Add two extra tests for git rebase

t/t3400-rebase.sh

@@ -14,7 +14,8 @@ export GIT_AUTHOR_EMAIL
 
 test_expect_success \
     'prepare repository with topic branches' \
-    'echo First > A &&
+    'git config core.logAllRefUpdates true &&
+     echo First > A &&
      git update-index --add A &&
      git commit -m "Add A." &&
      git checkout -b my-topic-branch &&
@@ -84,4 +85,14 @@ test_expect_success 'rebase a single mode change' '
      GIT_TRACE=1 git rebase master
 '
 
+test_expect_success 'HEAD was detached during rebase' '
+     test $(git rev-parse HEAD@{1}) != $(git rev-parse modechange@{1})
+'
+
+test_expect_success 'Show verbose error when HEAD could not be detached' '
+     : > B &&
+     test_must_fail git rebase topic 2> output.err > output.out &&
+     grep "Untracked working tree file .B. would be overwritten" output.err
+'
+
 test_done