failure_onion: a test that only ensures lightningd doesn't crash.

tests/plugins/htlc_accepted-failonion.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python3
+"""A simply plugin that fails HTLCs with a meaningless onion.
+
+"""
+from pyln.client import Plugin
+
+
+plugin = Plugin()
+
+
+@plugin.hook("htlc_accepted")
+def on_htlc_accepted(htlc, onion, plugin, **kwargs):
+    print('returning failonion', plugin.failonion)
+    return {"result": "fail", "failure_onion": plugin.failonion}
+
+
+@plugin.method("setfailonion")
+def setfailonion(plugin, onion):
+    """Sets the failure_onion to return when receiving an incoming HTLC.
+    """
+    plugin.failonion = onion
+
+
+@plugin.init()
+def on_init(**kwargs):
+    plugin.failonion = None
+
+
+plugin.run()