pytest: Add a test for htlc_accepted hook replay on startup

tests/plugins/hold_htlcs.py

@@ -0,0 +1,27 @@
+#!/usr/bin/env python3
+"""Plugin that holds on to HTLCs for 10 seconds.
+
+Used to test restarts / crashes while HTLCs were accepted, but not yet
+settled/forwarded/
+
+"""
+
+
+from lightning import Plugin
+import time
+
+
+plugin = Plugin()
+
+
+@plugin.hook("htlc_accepted")
+def on_htlc_accepted(htlc, onion, plugin):
+    plugin.log("Holding onto an incoming htlc for 10 seconds")
+    time.sleep(10)
+
+    # Give the tester something to look for
+    plugin.log("htlc_accepted hook called")
+    return {'result': 'continue'}
+
+
+plugin.run()