diff --git a/conntrackt/tests/test_models.py b/conntrackt/tests/test_models.py
--- a/conntrackt/tests/test_models.py
+++ b/conntrackt/tests/test_models.py
@@ -0,0 +1,70 @@
+# Django imports.
+from django.core.exceptions import ValidationError
+from django.db import IntegrityError
+from django.test import TestCase
+
+# Application imports.
+from conntrackt.models import Project, Location, Entity, Interface, Communication
+
+
+class EntityTest(TestCase):
+    fixtures = ['test-data.json']
+
+    def test_incoming_communications(self):
+        """
+        Test that we get correct list of incoming connections with the sample
+        data.
+        """
+
+        entity = Entity.objects.get(name="Test Entity 1")
+        incoming = Communication.objects.filter(pk__in=(1, 2, 3, 5))
+
+        self.assertItemsEqual(entity.incoming_communications(), incoming)
+
+    def test_outgoing_communications(self):
+        """
+        Test that we get correct list of outgoing connections with the sample
+        data.
+        """
+
+        entity = Entity.objects.get(name="Test Entity 1")
+        outgoing = Communication.objects.filter(pk__in=(4, 6))
+
+        self.assertItemsEqual(entity.outgoing_communications(), outgoing)
+
+    def test_unique_communication(self):
+        """
+        Test enforcement of unique communications.
+        """
+
+        comm = Communication.objects.get(pk=1)
+
+        self.assertRaises(IntegrityError, Communication.objects.create, source=comm.source, destination=comm.destination, protocol=comm.protocol, port=comm.port, description="Duplicate communication.")
+
+    def test_project_same(self):
+        """
+        Test enforcement of same project entities for communications.
+        """
+
+        ent1 = Entity.objects.get(name="Test Entity 1")
+        ent1_eth0 = ent1.interface_set.get(name="eth0")
+        ent2 = Entity.objects.get(name="Other Project Test Entity")
+        ent2_eth0 = ent2.interface_set.get(name="eth0")
+
+        # Set-up a communication between different projects.
+        comm = Communication.objects.create(source=ent1_eth0, destination=ent2_eth0, protocol="ICMP", port="8", description="Ping.")
+
+        self.assertRaises(ValidationError, comm.full_clean)
+
+    def test_unsupported_protocol(self):
+        """
+        Test enforcement of supported protocol.
+        """
+
+        ent1 = Entity.objects.get(name="Test Entity 1")
+        ent1_eth0 = ent1.interface_set.get(name="eth0")
+        ent2 = Entity.objects.get(name="Test Entity 2")
+        ent2_eth0 = ent1.interface_set.get(name="eth0")
+
+        comm = Communication(source=ent1_eth0, destination=ent2_eth0, protocol="BOGUS", port="1234")
+        self.assertRaises(ValidationError, comm.full_clean)