Commit c40ba8844e for bind

commit c40ba8844e9d08181a274394c582a5c4542b8680
Author: Ondřej Surý <ondrej@isc.org>
Date:   Thu Aug 13 09:16:08 2026 +0200

    Test duplicate singleton rejection

    Add FORMERR cases for identical duplicate SOA and CNAME records to the
    formerr system test.

    Assisted-by: Codex:gpt-5

diff --git a/bin/tests/system/formerr/tests_formerr.py b/bin/tests/system/formerr/tests_formerr.py
index b456de6248..dd9483d144 100644
--- a/bin/tests/system/formerr/tests_formerr.py
+++ b/bin/tests/system/formerr/tests_formerr.py
@@ -147,6 +147,15 @@ def soa_rr(
     )


+def cname_rr(*, target: bytes) -> bytes:
+    return rr(
+        root(),
+        dns.rdatatype.RdataType.CNAME,
+        dns.rdataclass.RdataClass.IN,
+        rdata=target,
+    )
+
+
 def nsec3_rr(
     *,
     owner: bytes,
@@ -342,6 +351,32 @@ def query_raw_tcp(host: str, port: int, packet_wire: bytes) -> bytes:
             ),
             id="dupans",
         ),
+        pytest.param(
+            wire(
+                header(qdcount=1, ancount=2),
+                question(root(), dns.rdatatype.RdataType.SOA),
+                soa_rr(minimum=5),
+                soa_rr(minimum=5),
+            ),
+            wire(
+                formerr_response_header(qdcount=1),
+                question(root(), dns.rdatatype.RdataType.SOA),
+            ),
+            id="dupans-identical-soa",
+        ),
+        pytest.param(
+            wire(
+                header(qdcount=1, ancount=2),
+                question(root(), dns.rdatatype.RdataType.CNAME),
+                cname_rr(target=name("target.")),
+                cname_rr(target=name("target.")),
+            ),
+            wire(
+                formerr_response_header(qdcount=1),
+                question(root(), dns.rdatatype.RdataType.CNAME),
+            ),
+            id="dupans-identical-cname",
+        ),
         pytest.param(
             wire(
                 header(ancount=1),