pylightning: Add a small test for async rpcmethods

Signed-off-by: Christian Decker <decker.christian@gmail.com>

tests/plugins/asynctest.py

@@ -0,0 +1,30 @@
+#!/usr/bin/env python3
+"""This plugin is used to check that async method calls are working correctly.
+
+The plugin registers a method `callme` with an argument. All calls are
+stashed away, and are only resolved on the fifth invocation. All calls
+will then return the argument of the fifth call.
+
+"""
+from lightning import Plugin
+
+plugin = Plugin()
+
+
+@plugin.init()
+def init(configuration, options, plugin):
+    plugin.requests = []
+
+
+@plugin.method('asyncqueue', sync=False)
+def async_queue(request, plugin):
+    plugin.requests.append(request)
+
+
+@plugin.method('asyncflush')
+def async_flush(res, plugin):
+    for r in plugin.requests:
+        r.set_result(res)
+
+
+plugin.run()