t5408, t5410: test duplicate updates without relying on the client

The existing t5408 tests that use send-pack to transmit duplicate
updates for the same destination happen to rely on the client not
recognizing the duplicates when the remote is empty.

As a result, they are the only push tests that exercise each of:

 - receive-pack rejection of multiple updates for the same ref, from
   9d2962a7c4 (receive-pack: use batched reference updates, 2025-05-19)

 - send-pack's receive_status() handling of a ref reported twice by the
   remote, from 77188b5bba (send-pack: fix memory leak around duplicate
   refs, 2025-05-19)

Add explicit tests for each of those paths, in preparation of an
upcoming commit that fixes the client to reject such pushes before
sending any update.

Signed-off-by: Jon Simons <jon@jonsimons.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5408-send-pack-stdin.sh

@@ -89,6 +89,18 @@ test_expect_success '--stdin refs come after cmdline' '
 	test_must_fail git --git-dir=remote.git rev-parse foo
 '
 
+test_expect_success 'send-pack handles repeated status for the same ref' '
+	clear_remote &&
+	test_hook -C remote.git receive-report <<-\EOF &&
+	cat >/dev/null &&
+	printf "%s\n" "unpack ok" "ng refs/heads/foo first" \
+		"ng refs/heads/foo second" 0000 |
+	test-tool pkt-line pack
+	EOF
+	test_must_fail git send-pack remote.git A:foo 2>err &&
+	test_grep "remote rejected.*A -> foo (second)" err
+'
+
 test_expect_success 'refspecs and --mirror do not mix (cmdline)' '
 	clear_remote &&
 	test_must_fail git send-pack remote.git --mirror $(cat refs)

t/t5410-receive-pack.sh

@@ -97,4 +97,39 @@ test_expect_success TEE_DOES_NOT_HANG \
 	test_must_fail git -C remote.git rev-list $(git -C repo rev-parse HEAD)
 '
 
+test_expect_success 'receive-pack rejects multiple updates for the same ref' '
+	test_when_finished "rm -rf repo remote.git" &&
+
+	git init repo &&
+	git -C repo commit --allow-empty -m A &&
+	git -C repo branch A &&
+	git -C repo commit --allow-empty -m B &&
+	git -C repo branch B &&
+	git init --bare remote.git &&
+	git -C repo send-pack ../remote.git A B &&
+	A=$(git -C repo rev-parse A) &&
+	B=$(git -C repo rev-parse B) &&
+	{
+		printf "%s %s refs/heads/foo\0report-status object-format=%s" \
+			$ZERO_OID $A "$(test_oid algo)" |
+		test-tool pkt-line pack-raw-stdin &&
+		printf "%s %s refs/heads/foo" $ZERO_OID $B |
+		test-tool pkt-line pack-raw-stdin &&
+		printf 0000 &&
+		git pack-objects --stdout </dev/null
+	} >request &&
+	git receive-pack remote.git <request >response 2>err &&
+	test_grep "multiple updates for ref ${SQ}refs/heads/foo${SQ} not allowed" err &&
+	test-tool pkt-line unpack <response >report &&
+	sed -n "/^unpack /,\$p" report >actual &&
+	cat >expect <<-\EOF &&
+	unpack ok
+	ng refs/heads/foo failed to update refs
+	ng refs/heads/foo failed to update refs
+	0000
+	EOF
+	test_cmp expect actual &&
+	test_must_fail git --git-dir=remote.git rev-parse --verify refs/heads/foo
+'
+
 test_done