tests: add test for multiple labels in BGP-LU

Announce three routes with label stacks 777/10006, 90, 11/22/33/44/55,
check that `show bgp ipv6 PREFIX json` has proper labels in
`remoteLabels`.

Test for issue #19506

Signed-off-by: Kyrylo Yatsenko <hedrok@gmail.com>

Author: hedrok

tests/topotests/bgp_lu_multiple_labels/__init__.py

@@ -0,0 +1,53 @@
+[exabgp.api]
+encoder = text
+highres = false
+respawn = false
+socket = ''
+
+[exabgp.bgp]
+openwait = 60
+
+[exabgp.cache]
+attributes = true
+nexthops = true
+
+[exabgp.daemon]
+daemonize = true
+pid = '/var/run/exabgp/exabgp.pid'
+user = 'exabgp'
+##daemonize = false
+
+[exabgp.log]
+all = false
+configuration = true
+daemon = true
+destination = '/var/log/exabgp.log'
+enable = true
+level = INFO
+message = false
+network = true
+packets = false
+parser = false
+processes = true
+reactor = true
+rib = false
+routes = false
+short = false
+timers = false
+
+[exabgp.pdb]
+enable = false
+
+[exabgp.profile]
+enable = false
+file = ''
+
+[exabgp.reactor]
+speed = 1.0
+
+[exabgp.tcp]
+acl = false
+bind = ''
+delay = 0
+once = false
+port = 179

tests/topotests/bgp_lu_multiple_labels/exabgp.env

@@ -0,0 +1,17 @@
+neighbor fc00::1 {
+    router-id 10.0.0.2;
+    local-address fc00::2;
+    local-as 65002;
+    peer-as 65001;
+    group-updates false;
+
+    family {
+        ipv6 nlri-mpls;
+    }
+
+    static {
+        route 2001:db8:100::/64 next-hop fc00::2 label [777 10006];
+        route 2001:db8:101::/64 next-hop fc00::2 label [90];
+        route 2001:db8:102::/64 next-hop fc00::2 label [11 22 33 44 55];
+    }
+}

tests/topotests/bgp_lu_multiple_labels/peer1/exabgp.cfg

@@ -0,0 +1,18 @@
+!
+interface r1-eth0
+ ip address fc00::1/64
+!
+router bgp 65001
+ bgp router-id 10.0.0.1
+ no bgp default ipv4-unicast
+ no bgp ebgp-requires-policy
+ neighbor fc00::2 remote-as external
+ neighbor fc00::2 timers 3 10
+ neighbor fc00::2 timers connect 1
+ address-family ipv6 unicast
+  no neighbor fc00::2 activate
+ exit-address-family
+ address-family ipv6 labeled-unicast
+  neighbor fc00::2 activate
+ exit-address-family
+!

tests/topotests/bgp_lu_multiple_labels/r1/frr.conf

@@ -0,0 +1,100 @@
+#!/usr/bin/env python
+# SPDX-License-Identifier: ISC
+
+#
+# Copyright (c) 2025 by
+# Kyrylo Yatsenko <hedrok@gmail.com>
+#
+
+"""
+"""
+
+import os
+import sys
+import json
+import pytest
+import functools
+
+CWD = os.path.dirname(os.path.realpath(__file__))
+sys.path.append(os.path.join(CWD, "../"))
+
+# pylint: disable=C0413
+from lib import topotest
+from lib.topogen import Topogen, get_topogen
+
+pytestmark = [pytest.mark.bgpd]
+
+
+def build_topo(tgen):
+    r1 = tgen.add_router("r1")
+    peer1 = tgen.add_exabgp_peer("peer1", ip="fc00::2/64", defaultRoute="via fc00::1")
+
+    switch = tgen.add_switch("s1")
+    switch.add_link(r1)
+    switch.add_link(peer1)
+
+
+def setup_module(mod):
+    tgen = Topogen(build_topo, mod.__name__)
+    tgen.start_topology()
+
+    for _, (rname, router) in enumerate(tgen.routers().items(), 1):
+        router.load_frr_config(os.path.join(CWD, "{}/frr.conf".format(rname)))
+
+    tgen.start_router()
+
+    peer = tgen.gears["peer1"]
+    peer.start(os.path.join(CWD, "peer1"), os.path.join(CWD, "exabgp.env"))
+
+
+def teardown_module(mod):
+    tgen = get_topogen()
+    tgen.stop_topology()
+
+
+
+def test_bgp_lu_multiple_labels():
+    tgen = get_topogen()
+
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    r1 = tgen.gears["r1"]
+
+    def _bgp_converge(prefix, labels):
+        output = json.loads(r1.vtysh_cmd(f"show bgp ipv6 {prefix} json"))
+        expected = {
+            "prefix": prefix,
+            "paths": [
+                {
+                    "valid": True,
+                    "nexthops": [{"ip": "fc00::2", "afi": "ipv6"}],
+                    "remoteLabels": labels,
+                },
+            ],
+        }
+        return topotest.json_cmp(output, expected)
+
+    test_func = functools.partial(_bgp_converge, '2001:db8:100::/64', [777, 10006])
+    _, result = topotest.run_and_expect(test_func, None, count=30, wait=1)
+    assert result is None, "2001:db8:100::/64 does not have expected labels"
+    test_func = functools.partial(_bgp_converge, '2001:db8:101::/64', [90])
+    _, result = topotest.run_and_expect(test_func, None, count=15, wait=1)
+    assert result is None, "2001:db8:101::/64 does not have expected labels"
+    test_func = functools.partial(_bgp_converge, '2001:db8:102::/64', [11, 22, 33, 44, 55])
+    _, result = topotest.run_and_expect(test_func, None, count=15, wait=1)
+    assert result is None, "2001:db8:102::/64 does not have expected labels"
+
+
+def test_memory_leak():
+    "Run the memory leak test and report results."
+    tgen = get_topogen()
+    if not tgen.is_memleak_enabled():
+        pytest.skip("Memory leak test/report is disabled")
+
+    tgen.report_memory_leaks()
+
+
+if __name__ == "__main__":
+    args = ["-s"] + sys.argv[1:]
+    sys.exit(pytest.main(args))