[nexus] migrate on-mesh prefix test to nexus (openthread#12963)

This commit migrates 'test_on_mesh_prefix.py' from the thread-cert
functional tests to the Nexus simulation framework.

The new Nexus test 'test_on_mesh_prefix.cpp' covers:
- Propagation of stable and non-stable on-mesh prefixes.
- Different Network Data request behavior for MEDs and SEDs.
- MEDs receiving both stable and non-stable prefixes.
- SEDs receiving only stable prefixes.
- IPv6 address configuration (SLAAC) for all prefixes.
- Reachability verification via ICMPv6 Echo Request/Response.

Migrating to Nexus provides faster execution and improves the
reliability of the functional test suite.

Author: jwhui

tests/nexus/CMakeLists.txt

@@ -406,6 +406,7 @@ ot_nexus_test(mle_blocking_downgrade "core;nexus")
 ot_nexus_test(mle_msg_key_seq_jump "core;nexus")
 ot_nexus_test(nat64_translator "core;nexus")
 ot_nexus_test(netdata_publisher "core;nexus")
+ot_nexus_test(on_mesh_prefix "core;nexus")
 ot_nexus_test(reed_address_solicit_rejected "core;nexus")
 ot_nexus_test(reset "core;nexus")
 ot_nexus_test(router_downgrade_on_sec_policy_change "core;nexus")

tests/nexus/test_on_mesh_prefix.cpp

@@ -0,0 +1,199 @@
+/*
+ *  Copyright (c) 2026, The OpenThread Authors.
+ *  All rights reserved.
+ *
+ *  Redistribution and use in source and binary forms, with or without
+ *  modification, are permitted provided that the following conditions are met:
+ *  1. Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *  2. Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *  3. Neither the name of the copyright holder nor the
+ *     names of its contributors may be used to endorse or promote products
+ *     derived from this software without specific prior written permission.
+ *
+ *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ *  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ *  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ *  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ *  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ *  POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <stdio.h>
+
+#include "mac/data_poll_sender.hpp"
+#include "platform/nexus_core.hpp"
+#include "platform/nexus_node.hpp"
+
+namespace ot {
+namespace Nexus {
+
+/**
+ * Time to advance for a node to form a network and become leader, in milliseconds.
+ */
+static constexpr uint32_t kFormNetworkTime = 13 * 1000;
+
+/**
+ * Time to advance for a node to join as a child and upgrade to a router, in milliseconds.
+ */
+static constexpr uint32_t kAttachToRouterTime = 200 * 1000;
+
+/**
+ * Time to advance for the network to stabilize after routers have attached.
+ */
+static constexpr uint32_t kStabilizationTime = 130 * 1000;
+
+static bool HasAddressWithPrefix(Node &aNode, const char *aPrefixString)
+{
+    Ip6::Prefix prefix;
+    bool        found = false;
+
+    SuccessOrQuit(prefix.FromString(aPrefixString));
+
+    for (const Ip6::Netif::UnicastAddress &addr : aNode.Get<ThreadNetif>().GetUnicastAddresses())
+    {
+        if (addr.GetAddress().MatchesPrefix(prefix))
+        {
+            found = true;
+            break;
+        }
+    }
+
+    return found;
+}
+
+void TestOnMeshPrefix(void)
+{
+    /**
+     * Test On-Mesh Prefix functionality.
+     *
+     * Topology:
+     *   LEADER <-> ROUTER <-> MED
+     *                  \ <-> SED
+     */
+
+    Core nexus;
+
+    Node &leader = nexus.CreateNode();
+    Node &router = nexus.CreateNode();
+    Node &med    = nexus.CreateNode();
+    Node &sed    = nexus.CreateNode();
+
+    leader.SetName("LEADER");
+    router.SetName("ROUTER");
+    med.SetName("MED");
+    sed.SetName("SED");
+
+    const char *kPrefix1 = "2001:2:0:1::/64";
+    const char *kPrefix2 = "2001:2:0:2::/64";
+    const char *kPrefix3 = "2002:2:0:3::/64";
+
+    AllowLinkBetween(leader, router);
+    AllowLinkBetween(router, med);
+    AllowLinkBetween(router, sed);
+
+    nexus.AdvanceTime(0);
+
+    SuccessOrQuit(Instance::SetGlobalLogLevel(kLogLevelNote));
+
+    Log("Step 1: Form network and attach nodes");
+    leader.Form();
+    nexus.AdvanceTime(kFormNetworkTime);
+    VerifyOrQuit(leader.Get<Mle::Mle>().IsLeader());
+
+    router.Join(leader, Node::kAsFtd);
+    med.Join(router, Node::kAsMed);
+    sed.Join(router, Node::kAsSed);
+
+    SuccessOrQuit(med.Get<DataPollSender>().SetExternalPollPeriod(1000));
+    SuccessOrQuit(sed.Get<DataPollSender>().SetExternalPollPeriod(1000));
+
+    nexus.AdvanceTime(kAttachToRouterTime);
+
+    VerifyOrQuit(router.Get<Mle::Mle>().IsRouter());
+    VerifyOrQuit(med.Get<Mle::Mle>().IsChild());
+    VerifyOrQuit(sed.Get<Mle::Mle>().IsChild());
+
+    Log("Step 2: Add prefixes on ROUTER");
+    // Prefix 1: 'paros' -> Preferred, SLAAC, Router, On-Mesh, Stable
+    {
+        NetworkData::OnMeshPrefixConfig config;
+        config.Clear();
+        SuccessOrQuit(config.GetPrefix().FromString(kPrefix1));
+        config.mPreferred = true;
+        config.mSlaac     = true;
+        config.mOnMesh    = true;
+        config.mStable    = true;
+        SuccessOrQuit(router.Get<NetworkData::Local>().AddOnMeshPrefix(config));
+    }
+
+    // Prefix 2: 'paro' -> Preferred, SLAAC, Router, On-Mesh, NOT Stable
+    {
+        NetworkData::OnMeshPrefixConfig config;
+        config.Clear();
+        SuccessOrQuit(config.GetPrefix().FromString(kPrefix2));
+        config.mPreferred = true;
+        config.mSlaac     = true;
+        config.mOnMesh    = true;
+        config.mStable    = false;
+        SuccessOrQuit(router.Get<NetworkData::Local>().AddOnMeshPrefix(config));
+    }
+
+    router.Get<NetworkData::Notifier>().HandleServerDataUpdated();
+    nexus.AdvanceTime(kStabilizationTime);
+
+    Log("Step 3: Verify addresses on MED and SED");
+    // MED should have both
+    VerifyOrQuit(HasAddressWithPrefix(med, kPrefix1));
+    VerifyOrQuit(HasAddressWithPrefix(med, kPrefix2));
+
+    // SED should have only Prefix 1 (stable)
+    VerifyOrQuit(HasAddressWithPrefix(sed, kPrefix1));
+    VerifyOrQuit(!HasAddressWithPrefix(sed, kPrefix2));
+
+    Log("Step 4: Verify pings from LEADER");
+    nexus.SendAndVerifyEchoRequest(leader, med.FindMatchingAddress(kPrefix1));
+    nexus.SendAndVerifyEchoRequest(leader, med.FindMatchingAddress(kPrefix2));
+    nexus.SendAndVerifyEchoRequest(leader, sed.FindMatchingAddress(kPrefix1));
+
+    Log("Step 5: Add prefix 3 (NOT On-Mesh)");
+    // Prefix 3: 'pars' -> Preferred, SLAAC, Router, Stable, NOT On-Mesh
+    {
+        NetworkData::OnMeshPrefixConfig config;
+        config.Clear();
+        SuccessOrQuit(config.GetPrefix().FromString(kPrefix3));
+        config.mPreferred = true;
+        config.mSlaac     = true;
+        config.mOnMesh    = false;
+        config.mStable    = true;
+        SuccessOrQuit(router.Get<NetworkData::Local>().AddOnMeshPrefix(config));
+    }
+
+    router.Get<NetworkData::Notifier>().HandleServerDataUpdated();
+    nexus.AdvanceTime(kStabilizationTime);
+
+    Log("Step 6: Verify address with Prefix 3 exists on MED and SED");
+    VerifyOrQuit(HasAddressWithPrefix(med, kPrefix3));
+    VerifyOrQuit(HasAddressWithPrefix(sed, kPrefix3));
+
+    nexus.SaveTestInfo("test_on_mesh_prefix.json");
+
+    Log("Test passed");
+}
+
+} // namespace Nexus
+} // namespace ot
+
+int main(void)
+{
+    ot::Nexus::TestOnMeshPrefix();
+    printf("All tests passed\n");
+    return 0;
+}