diff --git a/tests/unit/test_model.py b/tests/unit/test_model.py
new file mode 100644
index 0000000..222d881
--- /dev/null
+++ b/tests/unit/test_model.py
@@ -0,0 +1,155 @@
+import unittest
+
+import mock
+import asynctest
+
+
+def _make_delta(entity, type_, data=None):
+    from juju.client.client import Delta
+    from juju.delta import get_entity_delta
+
+    delta = Delta([entity, type_, data])
+    return get_entity_delta(delta)
+
+
+class TestObserver(unittest.TestCase):
+    def _make_observer(self, *args):
+        from juju.model import _Observer
+        return _Observer(*args)
+
+    def test_cares_about_id(self):
+        id_ = 'foo'
+
+        o = self._make_observer(
+            None, None, None, id_, None)
+
+        delta = _make_delta(
+            'application', 'change', dict(name=id_))
+
+        self.assertTrue(o.cares_about(delta))
+
+    def test_cares_about_type(self):
+        type_ = 'application'
+
+        o = self._make_observer(
+            None, type_, None, None, None)
+
+        delta = _make_delta(
+            type_, 'change', dict(name='foo'))
+
+        self.assertTrue(o.cares_about(delta))
+
+    def test_cares_about_action(self):
+        action = 'change'
+
+        o = self._make_observer(
+            None, None, action, None, None)
+
+        delta = _make_delta(
+            'application', action, dict(name='foo'))
+
+        self.assertTrue(o.cares_about(delta))
+
+    def test_cares_about_predicate(self):
+        def predicate(delta):
+            return delta.data.get('fizz') == 'bang'
+
+        o = self._make_observer(
+            None, None, None, None, predicate)
+
+        delta = _make_delta(
+            'application', 'change', dict(fizz='bang'))
+
+        self.assertTrue(o.cares_about(delta))
+
+
+class TestModelState(unittest.TestCase):
+    def test_apply_delta(self):
+        from juju.model import Model
+        from juju.application import Application
+
+        loop = mock.MagicMock()
+        model = Model(loop=loop)
+        delta = _make_delta('application', 'add', dict(name='foo'))
+
+        # test add
+        prev, new = model.state.apply_delta(delta)
+        self.assertEqual(
+            len(model.state.state[delta.entity][delta.get_id()]), 1)
+        self.assertIsNone(prev)
+        self.assertIsInstance(new, Application)
+
+        # test remove
+        delta.type = 'remove'
+        prev, new = model.state.apply_delta(delta)
+        # length of the entity history deque is now 3:
+        # - 1 for the first delta
+        # - 1 for the second delta
+        # - 1 for the None sentinel appended after the 'remove'
+        self.assertEqual(
+            len(model.state.state[delta.entity][delta.get_id()]), 3)
+        self.assertIsInstance(new, Application)
+        # new object is falsy because its data is None
+        self.assertFalse(new)
+        self.assertIsInstance(prev, Application)
+        self.assertTrue(prev)
+
+
+def test_get_series():
+    from juju.model import Model
+    model = Model()
+    entity = {
+        'Meta': {
+            'supported-series': {
+                'SupportedSeries': [
+                    'xenial',
+                    'trusty',
+                ],
+            },
+        },
+    }
+    assert model._get_series('cs:trusty/ubuntu', entity) == 'trusty'
+    assert model._get_series('xenial/ubuntu', entity) == 'xenial'
+    assert model._get_series('~foo/xenial/ubuntu', entity) == 'xenial'
+    assert model._get_series('~foo/ubuntu', entity) == 'xenial'
+    assert model._get_series('ubuntu', entity) == 'xenial'
+    assert model._get_series('cs:ubuntu', entity) == 'xenial'
+
+
+class TestContextManager(asynctest.TestCase):
+    @asynctest.patch('juju.model.Model.disconnect')
+    @asynctest.patch('juju.model.Model.connect_current')
+    async def test_normal_use(self, mock_connect, mock_disconnect):
+        from juju.model import Model
+
+        async with Model() as model:
+            self.assertTrue(isinstance(model, Model))
+
+        self.assertTrue(mock_connect.called)
+        self.assertTrue(mock_disconnect.called)
+
+    @asynctest.patch('juju.model.Model.disconnect')
+    @asynctest.patch('juju.model.Model.connect_current')
+    async def test_exception(self, mock_connect, mock_disconnect):
+        from juju.model import Model
+
+        class SomeException(Exception):
+            pass
+
+        with self.assertRaises(SomeException):
+            async with Model():
+                raise SomeException()
+
+        self.assertTrue(mock_connect.called)
+        self.assertTrue(mock_disconnect.called)
+
+    @asynctest.patch('juju.client.connection.JujuData.current_controller')
+    async def test_no_current_connection(self, mock_current_controller):
+        from juju.model import Model
+        from juju.errors import JujuConnectionError
+
+        mock_current_controller.return_value = ""
+
+        with self.assertRaises(JujuConnectionError):
+            async with Model():
+                pass