Add mdns unit tests for main service handler

At the midcycle we discussed improving the test suite. When writing
tests for ALIAS records, I ran into some dependencies that weren't
necessary. These tests are a start to allow small refactorings to
allow more incremental improvements to the code and require less
setup/teardown over time.

More specifically, this lazily loads the central api instance, allowing
it to be overridden in tests as well as providing clarification seen in
a comment regarding what DNS opcodes we actually support.

Change-Id: I065811c9cc22cd44d729f1578733514250cd3c71

designate/tests/unit/test_mdns/test_handler.py

@@ -0,0 +1,106 @@
+# Copyright 2014 Rackspace Inc.
+#
+# Author: Eric Larson <eric.larson@rackspace.com>
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+import unittest
+
+import dns
+from mock import Mock
+
+from designate.mdns import handler
+
+
+class TestRequestHandlerCall(unittest.TestCase):
+    """
+    Unit test to assert the dispatching based on the request
+    operation.
+    """
+
+    def setUp(self):
+        self.storage = Mock()
+        self.tg = Mock()
+        self.handler = handler.RequestHandler(self.storage, self.tg)
+
+        # Use a simple handlers that doesn't require a real request
+        self.handler._handle_query_error = Mock(return_value='Error')
+        self.handler._handle_axfr = Mock(return_value=['AXFR'])
+        self.handler._handle_record_query = Mock(return_value=['Record Query'])
+        self.handler._handle_notify = Mock(return_value=['Notify'])
+
+    def assert_error(self, request, error_type):
+        self.handler._handle_query_error.assert_called_with(
+            request, error_type
+        )
+        return True
+
+    def test_central_api_property(self):
+        self.handler._central_api = 'foo'
+        assert self.handler.central_api == 'foo'
+
+    def test___call___unhandled_opcodes(self):
+        unhandled_codes = [
+            dns.opcode.STATUS,
+            dns.opcode.IQUERY,
+            dns.opcode.UPDATE,
+        ]
+
+        request = Mock()
+        for code in unhandled_codes:
+            request.opcode.return_value = code  # return an error
+            assert list(self.handler(request)) == ['Error']
+            self.assert_error(request, dns.rcode.REFUSED)
+
+    def test___call__query_error_with_more_than_one_question(self):
+        request = Mock()
+        request.opcode.return_value = dns.opcode.QUERY
+        request.question = [Mock(), Mock()]
+
+        assert list(self.handler(request)) == ['Error']
+        self.assert_error(request, dns.rcode.REFUSED)
+
+    def test___call__query_error_with_data_claas_not_in(self):
+        request = Mock()
+        request.opcode.return_value = dns.opcode.QUERY
+        request.question = [Mock(rdclass=dns.rdataclass.ANY)]
+        assert list(self.handler(request)) == ['Error']
+        self.assert_error(request, dns.rcode.REFUSED)
+
+    def test___call__axfr(self):
+        request = Mock()
+        request.opcode.return_value = dns.opcode.QUERY
+        request.question = [
+            Mock(rdclass=dns.rdataclass.IN, rdtype=dns.rdatatype.AXFR)
+        ]
+        assert list(self.handler(request)) == ['AXFR']
+
+    def test___call__ixfr(self):
+        request = Mock()
+        request.opcode.return_value = dns.opcode.QUERY
+        request.question = [
+            Mock(rdclass=dns.rdataclass.IN, rdtype=dns.rdatatype.IXFR)
+        ]
+        assert list(self.handler(request)) == ['AXFR']
+
+    def test___call__record_query(self):
+        request = Mock()
+        request.opcode.return_value = dns.opcode.QUERY
+        request.question = [
+            Mock(rdclass=dns.rdataclass.IN, rdtype=dns.rdatatype.A)
+        ]
+        assert list(self.handler(request)) == ['Record Query']
+
+    def test___call__notify(self):
+        request = Mock()
+        request.opcode.return_value = dns.opcode.NOTIFY
+        assert list(self.handler(request)) == ['Notify']