L2SS-291: Separate abstract device class across files and test

devices/devices/abstract_device.py

+# -*- coding: utf-8 -*-
+#
+# This file is part of the XXX project
+#
+#
+#
+# Distributed under the terms of the APACHE license.
+# See LICENSE.txt for more info.
+
+"""Abstract Device Meta for LOFAR2.0
+
+"""
+
+from abc import ABCMeta
+import logging
+
+from tango.server import DeviceMeta
+
+logger = logging.getLogger()
+
+
+class AbstractDeviceMetas(DeviceMeta, ABCMeta):
+    """Collects meta classes to allow hardware_device to be both a Device and an ABC. """
+
+    def __new__(mcs, name, bases, namespace, **kwargs):
+        cls = ABCMeta.__new__(mcs, name, bases, namespace, **kwargs)
+        cls = DeviceMeta.__new__(type(cls), name, bases, namespace)
+        return cls

devices/devices/hardware_device.py

@@ -20,18 +20,15 @@ from tango import DevState, DebugIt, Attribute, DeviceProxy
 
 from clients.attribute_wrapper import attribute_wrapper
 from common.lofar_logging import log_exceptions
-import logging
+from devices.abstract_device import AbstractDeviceMetas
+from devices.device_decorators import only_in_states, fault_on_error
 
+import logging
 
 __all__ = ["hardware_device"]
 
-from devices.device_decorators import only_in_states, fault_on_error
-
 logger = logging.getLogger()
 
-class AbstractDeviceMetas(DeviceMeta, ABCMeta):
-    ''' Collects meta classes to allow hardware_device to be both a Device and an ABC. '''
-    pass
 
 #@log_exceptions()
 class hardware_device(Device, metaclass=AbstractDeviceMetas):

devices/test/devices/test_abstract_device.py

+# -*- coding: utf-8 -*-
+#
+# This file is part of the LOFAR 2.0 Station Software
+#
+#
+#
+# Distributed under the terms of the APACHE license.
+# See LICENSE.txt for more info.
+
+import abc
+from unittest import mock
+
+from tango import DevFailed
+from tango import server
+from tango.server import attribute
+
+from tango.test_context import DeviceTestContext
+
+from devices.abstract_device import AbstractDeviceMetas
+
+from test import base
+
+
+class TestAbstractDevice(base.TestCase):
+
+    class AbstractExample(object, metaclass=abc.ABCMeta):
+        """A pure abc.ABCMeta metaclass with an abstract method
+
+        This is an abstract class that inherits object with the abc.ABCMeta as
+        metaclass
+        """
+
+        @abc.abstractmethod
+        def example_method(self):
+            raise NotImplementedError
+
+    class TestHardwareDevice(server.Device, metaclass=AbstractDeviceMetas):
+        """This is your overarching abstract class with a combined metaclass
+
+        Device is an object with DeviceMeta as metaclass
+        We use HardwareDeviceMetas as metaclass
+
+        Our metaclass contract is now fulfilled.
+        """
+
+        @attribute(dtype=float)
+        def call_example_method(self):
+            return self.example_method()
+
+        @abc.abstractmethod
+        def example_method(self):
+            raise NotImplementedError
+
+    class ConcreteHardwareDevice(TestHardwareDevice):
+
+        def example_method(self):
+            return 12
+
+    def setUp(self):
+        super(TestAbstractDevice, self).setUp()
+
+    def test_instance_tango(self):
+
+        try:
+            with DeviceTestContext(self.TestHardwareDevice, process=True) as proxy:
+                # Calling this method raises the NotImplementedError exception
+                proxy.call_example_method()
+        except Exception as e:
+            self.assertIsInstance(e, DevFailed)
+
+        with DeviceTestContext(self.ConcreteHardwareDevice, process=True) as proxy:
+            self.assertEqual(12, proxy.call_example_method)
+
+    @mock.patch.object(server, 'get_worker')
+    @mock.patch.object(server, 'LatestDeviceImpl')
+    def test_instance_error(self, m_worker, m_implement):
+        # Creating this object should raise a type error but it does not
+        # combining metaclasses in this way does not have the desired result.
+        # This is a known limitation of this approach
+        m_device = self.TestHardwareDevice(mock.Mock(), mock.Mock())
+
+        # Raising the NotImplementedError works as expected, however.
+        self.assertRaises(NotImplementedError, m_device.example_method)
+
+        # Creating this object of a class that has a pure metaclass does raise
+        # the expected error.
+        self.assertRaises(TypeError, self.AbstractExample)
+
+