pytest: test the invoice hook.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tests/plugins/reject_some_invoices.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+"""Simple plugin to test the invoice_payment_hook.
+
+We just refuse to let them pay invoices with preimages divisible by 16.
+"""
+
+from lightning import Plugin
+
+plugin = Plugin()
+
+
+@plugin.hook('invoice_payment')
+def on_payment(payment, plugin):
+    print("label={}".format(payment['label']))
+    print("msat={}".format(payment['msat']))
+    print("preimage={}".format(payment['preimage']))
+
+    if payment['preimage'].endswith('0'):
+        # FIXME: Define this!
+        WIRE_TEMPORARY_NODE_FAILURE = 0x2002
+        return {'result': {'failure_code': WIRE_TEMPORARY_NODE_FAILURE}}
+
+    return {'result': {}}
+
+
+plugin.run()