pytest: test pay during channel open

Notably this parses the listpeerchannels output while the state is
still uncommitted, i.e., state = OPENINGD.

tests/plugins/openchannel_hook_delay.py

@@ -0,0 +1,32 @@
+#!/usr/bin/env python3
+"""Plugin to test openchannel_hook
+
+Will simply accept any channel. Useful fot testing chained hook.
+"""
+
+from pyln.client import Plugin
+import time
+
+plugin = Plugin()
+
+
+@plugin.hook('openchannel')
+def on_openchannel(openchannel, plugin, **kwargs):
+    delaytime = float(plugin.get_option('delaytime'))
+    msg = f'delaying WIRE_ACCEPT_CHANNEL for {delaytime}s'
+    plugin.log(msg)
+    time.sleep(delaytime)
+    return {'result': 'continue'}
+
+
+@plugin.hook('openchannel2')
+def on_openchannel2(openchannel2, plugin, **kwargs):
+    delaytime = float(plugin.get_option('delaytime'))
+    msg = f'delaying WIRE_ACCEPT_CHANNEL for {delaytime}s'
+    plugin.log(msg)
+    time.sleep(delaytime)
+    return {'result': 'continue'}
+
+
+plugin.add_option('delaytime', '10', 'How long to hold the WIRE_OPEN_CHANNEL.')
+plugin.run()

tests/test_pay.py

@@ -5588,3 +5588,20 @@ def test_pay_partial_msat(node_factory, executor):
 
     l1pay.result(TIMEOUT)
     l3pay.result(TIMEOUT)
+
+
+@pytest.mark.xfail(strict=True)
+def test_pay_while_opening_channel(node_factory, bitcoind, executor):
+    delay_plugin = {'plugin': os.path.join(os.getcwd(),
+                                           'tests/plugins/openchannel_hook_delay.py'),
+                    'delaytime': '10'}
+    l1, l2 = node_factory.line_graph(2, fundamount=10**6, wait_for_announce=True)
+    l3 = node_factory.get_node(options=delay_plugin)
+    l1.connect(l3)
+    executor.submit(l1.rpc.fundchannel, l3.info['id'], 100000)
+    wait_for(lambda: l1.rpc.listpeerchannels(l3.info['id'])['channels'] != [])
+
+    # the uncommitted channel should now show up in listpeerchannels
+    assert only_one(l1.rpc.listpeerchannels(l3.info['id'])['channels'])['state'] == 'OPENINGD'
+    inv = l2.rpc.invoice(10000, "inv", "inv")
+    l1.rpc.pay(inv['bolt11'])