diff --git a/dbtemplates/test_signal_handlers.py b/dbtemplates/test_signal_handlers.py
new file mode 100644
index 0000000..2608048
--- /dev/null
+++ b/dbtemplates/test_signal_handlers.py
@@ -0,0 +1,80 @@
+from django.contrib.sites.models import Site
+from django.db.models.signals import m2m_changed
+from django.db.utils import IntegrityError
+from django.dispatch import receiver
+from django.test import TestCase, override_settings
+from django.test.signals import setting_changed
+
+from dbtemplates.models import Template
+
+
+@receiver(setting_changed)
+def reload_modules_when_settings_change(sender, setting, value, enter, **kwargs):
+    from .signal_handlers import verify_template_name_uniqueness_across_all_selected_sites
+    if setting == 'DBTEMPLATES_UNIQUE' and value:
+        if enter:
+            m2m_changed.connect(verify_template_name_uniqueness_across_all_selected_sites)
+        else:
+            m2m_changed.disconnect(verify_template_name_uniqueness_across_all_selected_sites)
+
+
+class VerifyTemplateUniqueness(TestCase):
+    @classmethod
+    def setUpTestData(cls):
+        sites = Site.objects.bulk_create([
+            Site(name="All", domain="all.example.com"),
+            Site(name="1", domain="one.example.com"),
+            Site(name="2", domain="two.example.com"),
+            Site(name="3", domain="three.example.com"),
+        ])
+
+        templates = Template.objects.bulk_create([
+            Template(name="Ayy", content="AAAA"),
+            Template(name="Bee", content="BBBB"),
+            Template(name="Sea", content="CCCC"),
+            Template(name="Dee", content="AAAA"),
+            Template(name="Eee", content="AAAA"),
+            Template(name="Ayy", content="FFFF"),
+            Template(name="Bee", content="GGGG"),
+        ])
+
+        for template in templates[:3]:
+            template.sites.add(sites[0])
+
+        templates[0].sites.add(sites[1])
+        templates[1].sites.add(sites[2])
+        templates[2].sites.add(sites[3])
+
+        cls.sites = sites
+        cls.templates = templates
+
+    @override_settings(
+        DBTEMPLATES_UNIQUE=True,
+        DBTEMPLATES_ADD_DEFAULT_SITE=False,
+    )
+    def test_signal_handler_forward_unique_works(self):
+        self.templates[0].sites.add(self.sites[2])
+        self.templates[3].sites.add(self.sites[0])
+
+    @override_settings(
+        DBTEMPLATES_UNIQUE=True,
+        DBTEMPLATES_ADD_DEFAULT_SITE=False,
+    )
+    def test_signal_handler_reverse_unique_works(self):
+        self.sites[3].template_set.add(self.templates[1])
+
+    @override_settings(
+        DBTEMPLATES_UNIQUE=True,
+        DBTEMPLATES_ADD_DEFAULT_SITE=False,
+    )
+    def test_signal_handler_forward_nonunique_prevented(self):
+        with self.assertRaises(IntegrityError):
+            self.templates[5].sites.add(self.sites[0])
+
+    @override_settings(
+        DBTEMPLATES_UNIQUE=True,
+        DBTEMPLATES_ADD_DEFAULT_SITE=False,
+    )
+    def test_signal_handler_reverse_nonunique_prevented(self):
+        with self.assertRaises(IntegrityError):
+            self.sites[2].template_set.add(self.templates[6])