test_expect_success 'Show verbose error when HEAD could not be detached' '
>B &&
+ test_when_finished "rm -f B" &&
test_must_fail git rebase topic 2>output.err >output.out &&
test_i18ngrep "The following untracked working tree files would be overwritten by checkout:" output.err &&
test_i18ngrep B output.err
'
-rm -f B
test_expect_success 'fail when upstream arg is missing and not on branch' '
git checkout topic &&
test_must_be_empty err
'
+test_expect_success 'switch to branch checked out here' '
+ git checkout master &&
+ git rebase master master
+'
+
+test_expect_success 'switch to branch not checked out' '
+ git checkout master &&
+ git branch other &&
+ git rebase master other
+'
+
+test_expect_success 'refuse to switch to branch checked out elsewhere' '
+ git checkout master &&
+ git worktree add wt &&
+ test_must_fail git -C wt rebase master master 2>err &&
+ test_i18ngrep "already checked out" err
+'
+
test_done