t3400: demonstrate failure with format.useAutoBase

Ever since bb52995 (format-patch: introduce format.useAutoBase
configuration, 2016-04-26), `git rebase` has been broken when
`format.useAutoBase = true`. It fails when rebasing a branch:

	fatal: failed to get upstream, if you want to record base commit automatically,
	please use git branch --set-upstream-to to track a remote branch.
	Or you could specify base commit by --base=<base-commit-id> manually
	error:
	git encountered an error while preparing the patches to replay
	these revisions:

	    ede2467cdedc63784887b587a61c36b7850ebfac..d8f581194799ae29bf5fa72a98cbae98a1198b12

	As a result, git cannot rebase them.

Demonstrate that failure here.

Reported-by: Christian Biesinger <[email protected]>
Signed-off-by: Denton Liu <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: Denton-L

t/t3400-rebase.sh

@@ -159,6 +159,12 @@ test_expect_success 'fail when upstream arg is missing and not configured' '
 	test_must_fail git rebase
 '
 
+test_expect_failure 'rebase works with format.useAutoBase' '
+	test_config format.useAutoBase true &&
+	git checkout topic &&
+	git rebase master
+'
+
 test_expect_success 'default to common base in @{upstream}s reflog if no upstream arg' '
 	git checkout -b default-base master &&
 	git checkout -b default topic &&