+test_expect_success 'errors if given a bad branch name' '
+ cat <<-\EOF >expect &&
+ fatal: '\''foo..bar'\'' is not a valid branch name
+ hint: See `man git check-ref-format`
+ hint: Disable this message with "git config advice.refSyntax false"
+ EOF
+ test_must_fail git branch foo..bar >actual 2>&1 &&
+ test_cmp expect actual
+'
+