diff --git a/.coveragerc b/.coveragerc
index ba44c433..9a767c99 100644
--- a/.coveragerc
+++ b/.coveragerc
@@ -16,6 +16,7 @@ omit =
     *kombu/transport/sqlalchemy/*
     *kombu/utils.compat.py
     *kombu/utils/eventio.py
+    *kombu/async/debug.py
     *kombu/transport/amqplib.py
     *kombu/transport/couchdb.py
     *kombu/transport/beanstalk.py
diff --git a/kombu/tests/async/test_hub.py b/kombu/tests/async/test_hub.py
index 1c792381..94cf6b04 100644
--- a/kombu/tests/async/test_hub.py
+++ b/kombu/tests/async/test_hub.py
@@ -2,6 +2,8 @@ from __future__ import absolute_import, unicode_literals
 
 import errno
 
+from vine import promise
+
 from kombu.async import hub as _hub
 from kombu.async import Hub, READ, WRITE, ERR
 from kombu.async.debug import callback_for, repr_flag, _rcb
@@ -184,6 +186,20 @@ class test_Hub(Case):
         self.hub.stop()
         self.hub.call_soon.assert_called_with(_raise_stop_error)
 
+    @patch('kombu.async.hub.promise')
+    def test_call_soon(self, promise):
+        callback = Mock(name='callback')
+        ret = self.hub.call_soon(callback, 1, 2, 3)
+        promise.assert_called_with(callback, (1, 2, 3))
+        self.assertIn(promise(), self.hub._ready)
+        self.assertIs(ret, promise())
+
+    def test_call_soon__promise_argument(self):
+        callback = promise(Mock(name='callback'), (1, 2, 3))
+        ret = self.hub.call_soon(callback)
+        self.assertIs(ret, callback)
+        self.assertIn(ret, self.hub._ready)
+
     def test_call_later(self):
         callback = Mock(name='callback')
         self.hub.timer = Mock(name='hub.timer')
@@ -318,6 +334,12 @@ class test_Hub(Case):
         self.assertNotIn(2, self.hub.readers)
         self.assertIn(2, self.hub.writers)
 
+    def test_remove_reader__not_writeable(self):
+        self.hub.poller = Mock(name='hub.poller')
+        self.hub.add(2, Mock(), READ)
+        self.hub.remove_reader(2)
+        self.assertNotIn(2, self.hub.readers)
+
     def test_remove_writer(self):
         self.hub.poller = Mock(name='hub.poller')
         self.hub.add(2, Mock(), READ)
@@ -326,6 +348,12 @@ class test_Hub(Case):
         self.assertIn(2, self.hub.readers)
         self.assertNotIn(2, self.hub.writers)
 
+    def test_remove_writer__not_readable(self):
+        self.hub.poller = Mock(name='hub.poller')
+        self.hub.add(2, Mock(), WRITE)
+        self.hub.remove_writer(2)
+        self.assertNotIn(2, self.hub.writers)
+
     def test_add__consolidate(self):
         self.hub.poller = Mock(name='hub.poller')
         self.hub.add(2, Mock(), WRITE, consolidate=True)
@@ -477,3 +505,31 @@ class test_Hub(Case):
     def test_scheduler_property(self):
         hub = Hub(timer=[1, 2, 3])
         self.assertEqual(list(hub.scheduler), [1, 2, 3])
+
+    def test_loop__tick_callbacks(self):
+        self.hub._ready = Mock(name='_ready')
+        self.hub._ready.pop.side_effect = RuntimeError()
+        ticks = [Mock(name='cb1'), Mock(name='cb2')]
+        self.hub.on_tick = list(ticks)
+
+        with self.assertRaises(RuntimeError):
+            next(self.hub.loop)
+
+        ticks[0].assert_called_once_with()
+        ticks[1].assert_called_once_with()
+
+    def test_loop__todo(self):
+        self.hub.fire_timers = Mock(name='fire_timers')
+        self.hub.fire_timers.side_effect = RuntimeError()
+        self.hub.timer = Mock(name='timer')
+
+        callbacks = [Mock(name='cb1'), Mock(name='cb2')]
+        for cb in callbacks:
+            self.hub.call_soon(cb)
+        self.hub._ready.add(None)
+
+        with self.assertRaises(RuntimeError):
+            next(self.hub.loop)
+
+        callbacks[0].assert_called_once_with()
+        callbacks[1].assert_called_once_with()
diff --git a/kombu/tests/async/test_timer.py b/kombu/tests/async/test_timer.py
index 94b5fddf..f52fc93e 100644
--- a/kombu/tests/async/test_timer.py
+++ b/kombu/tests/async/test_timer.py
@@ -1,5 +1,7 @@
 from __future__ import absolute_import, unicode_literals
 
+from datetime import datetime
+
 from kombu.five import bytes_if_py2
 
 from kombu.async.timer import Entry, Timer, to_timestamp
@@ -9,9 +11,12 @@ from kombu.tests.case import Case, Mock, mock, patch
 
 class test_to_timestamp(Case):
 
-    def test_to_timestamp(self):
+    def test_timestamp(self):
         self.assertIs(to_timestamp(3.13), 3.13)
 
+    def test_datetime(self):
+        self.assertTrue(to_timestamp(datetime.utcnow()))
+
 
 class test_Entry(Case):