! grep "^ fileX | *1 +$" diffstat.txt
'
+# Output to stderr:
+#
+# "Does not point to a valid commit: invalid-ref"
+#
+# NEEDSWORK: This "grep" is fine in real non-C locales, but
+# GETTEXT_POISON poisons the refname along with the enclosing
+# error message.
+test_expect_success 'rebase --onto outputs the invalid ref' '
+ test_must_fail git rebase --onto invalid-ref HEAD HEAD 2>err &&
+ test_i18ngrep "invalid-ref" err
+'
+
test_done