pytest: Add a simple test for the hooks

This uses the `htlc_accepted` hook to delay payment acceptance.

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

contrib/plugins/helloworld.py

@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
 from lightning import Plugin
-
+import time
 
 plugin = Plugin()
 
@@ -34,5 +34,12 @@ def on_disconnect(plugin, id):
     plugin.log("Received disconnect event for peer {}".format(id))
 
 
+@plugin.hook("htlc_accepted")
+def on_htlc_accepted(plugin):
+    plugin.log('on_htlc_accepted called')
+    time.sleep(20)
+    return None
+
+
 plugin.add_option('greeting', 'Hello', 'The greeting I should use.')
 plugin.run()

tests/test_plugin.py

@@ -107,6 +107,26 @@ def test_plugin_disable(node_factory):
         n.rpc.hello(name='Sun')
 
 
+def test_plugin_hook(node_factory, executor):
+    """The helloworld plugin registers a htlc_accepted hook.
+
+    The hook will sleep for a few seconds and log a
+    message. `lightningd` should wait for the response and only then
+    complete the payment.
+
+    """
+    l1, l2 = node_factory.line_graph(2, opts={'plugin': 'contrib/plugins/helloworld.py'})
+    start_time = time.time()
+    f = executor.submit(l1.pay, l2, 100000)
+    l2.daemon.wait_for_log(r'on_htlc_accepted called')
+
+    # The hook will sleep for 20 seconds before answering, so `f`
+    # should take at least that long.
+    f.result()
+    end_time = time.time()
+    assert(end_time >= start_time + 20)
+
+
 def test_plugin_notifications(node_factory):
     l1, l2 = node_factory.get_nodes(2, opts={'plugin': 'contrib/plugins/helloworld.py'})