tests: lnpeer: test_reject_payment_for_expired_invoice

diff --git a/tests/test_lnpeer.py b/tests/test_lnpeer.py
index 2a86f5d..e5f98ec 100644
--- a/tests/test_lnpeer.py
+++ b/tests/test_lnpeer.py
@@ -11,6 +11,7 @@ import concurrent
 from concurrent import futures
 from unittest import mock
 from typing import Iterable, NamedTuple, Tuple, List, Dict, Sequence
+import time
 
 from aiorpcx import timeout_after, TaskTimeout
 from electrum_ecc import ECPrivkey
@@ -559,6 +560,7 @@ class TestPeer(ElectrumTestCase):
             payment_hash: bytes = None,
             invoice_features: LnFeatures = None,
             min_final_cltv_delta: int = None,
+            expiry: int = None,
     ) -> Tuple[LnAddr, Invoice]:
         amount_btc = amount_msat/Decimal(COIN*1000)
         if payment_preimage is None and not payment_hash:
@@ -586,7 +588,7 @@ class TestPeer(ElectrumTestCase):
             direction=RECEIVED,
             status=PR_UNPAID,
             min_final_cltv_delta=min_final_cltv_delta,
-            expiry_delay=LN_EXPIRY_NEVER,
+            expiry_delay=expiry or LN_EXPIRY_NEVER,
         )
         w2.save_payment_info(info)
         lnaddr1 = LnAddr(
@@ -596,6 +598,7 @@ class TestPeer(ElectrumTestCase):
                 ('c', min_final_cltv_delta),
                 ('d', 'coffee'),
                 ('9', invoice_features),
+                ('x', expiry or 3600),
             ] + routing_hints,
             payment_secret=payment_secret,
         )
@@ -1000,6 +1003,49 @@ class TestPeerDirect(TestPeer):
         for _test_trampoline in [False, True]:
             await run_test(_test_trampoline)
 
+    async def test_reject_payment_for_expired_invoice(self):
+        """Tests that new htlcs paying an invoice that has already been expired will get rejected."""
+        async def run_test(test_trampoline):
+            alice_channel, bob_channel = create_test_channels()
+            p1, p2, w1, w2, _q1, _q2 = self.prepare_peers(alice_channel, bob_channel)
+
+            # create lightning invoice in the past, so it is expired
+            with mock.patch('time.time', return_value=int(time.time()) - 10000):
+                lnaddr, _pay_req = self.prepare_invoice(w2, expiry=3600)
+                b11 = lnencode(lnaddr, w2.node_keypair.privkey)
+                pay_req = Invoice.from_bech32(b11)
+
+            async def try_pay_expired_invoice(pay_req: Invoice, w1=w1):
+                assert pay_req.has_expired()
+                assert lnaddr.is_expired()
+                with mock.patch.object(w1, "_check_bolt11_invoice", return_value=lnaddr):
+                    result, log = await w1.pay_invoice(pay_req)
+                if not result:
+                    raise PaymentFailure()
+                raise PaymentDone()
+
+            if test_trampoline:
+                await self._activate_trampoline(w1)
+                # declare bob as trampoline node
+                electrum.trampoline._TRAMPOLINE_NODES_UNITTESTS = {
+                    'bob': LNPeerAddr(host="127.0.0.1", port=9735, pubkey=w2.node_keypair.pubkey),
+                }
+
+            async def f():
+                async with OldTaskGroup() as group:
+                    await group.spawn(p1._message_loop())
+                    await group.spawn(p1.htlc_switch())
+                    await group.spawn(p2._message_loop())
+                    await group.spawn(p2.htlc_switch())
+                    await asyncio.sleep(0.01)
+                    await group.spawn(try_pay_expired_invoice(pay_req))
+
+            with self.assertRaises(PaymentFailure):
+                await f()
+
+        for _test_trampoline in [False, True]:
+            await run_test(_test_trampoline)
+
     async def test_payment_race(self):
         """Alice and Bob pay each other simultaneously.
         They both send 'update_add_htlc' and receive each other's update