diff --git a/wiki_groups/tests.py b/wiki_groups/tests.py
index 7ce503c..662c669 100644
--- a/wiki_groups/tests.py
+++ b/wiki_groups/tests.py
@@ -1,3 +1,154 @@
+from django.contrib.auth import get_user_model
+from django.contrib.auth.models import Group
 from django.test import TestCase
 
-# Create your tests here.
+from wiki_groups.models import WikiGroup
+
+User = get_user_model()
+
+
+def create_user(username):
+    return User.objects.create_user(username=username)
+
+
+def create_group(name, with_users=None):
+    """Create a new WikiGroup, initialised with some new Users."""
+    django_group = Group.objects.create(name=name)
+    wiki_group = WikiGroup.objects.create(django_group=django_group)
+    if with_users is not None:
+        for username in with_users:
+            u = create_user(username)
+            wiki_group.users.add(u)
+    return wiki_group
+
+
+class TestPropagation(TestCase):
+    """Test that WikiGroup changes are correctly propagated to normal Django groups."""
+
+    def test_tree(self):
+        """Simple case: tree-shaped group structure."""
+        a = create_group("group_a", with_users=["a1", "a2"])
+        b = create_group("group_b", with_users=["b1", "b2"])
+        c = create_group("group_c", with_users=["c1", "c2"])
+
+        a.includes_groups.set([b, c])
+
+        self.assertQuerysetEqual(
+            a.django_group.user_set.all(), map(repr, User.objects.all()), ordered=False,
+        )
+        self.assertQuerysetEqual(
+            b.django_group.user_set.all(),
+            ["b1", "b2"],
+            ordered=False,
+            transform=lambda u: u.username,
+        )
+        self.assertQuerysetEqual(
+            c.django_group.user_set.all(),
+            ["c1", "c2"],
+            ordered=False,
+            transform=lambda u: u.username,
+        )
+
+    def test_diamond(self):
+        """Simple case: diamond-shaped group structure."""
+        a = create_group("group_a", with_users=["a1", "a2"])
+        b = create_group("group_b", with_users=["b1", "b2"])
+        c = create_group("group_c", with_users=["c1", "c2"])
+        d = create_group("group_d", with_users=["d1", "d2"])
+
+        a.includes_groups.set([b, c])
+        b.includes_groups.add(d)
+        c.includes_groups.add(d)
+
+        self.assertQuerysetEqual(
+            a.django_group.user_set.all(), map(repr, User.objects.all()), ordered=False,
+        )
+        self.assertQuerysetEqual(
+            b.django_group.user_set.all(),
+            ["b1", "b2", "d1", "d2"],
+            ordered=False,
+            transform=lambda u: u.username,
+        )
+        self.assertQuerysetEqual(
+            c.django_group.user_set.all(),
+            ["c1", "c2", "d1", "d2"],
+            ordered=False,
+            transform=lambda u: u.username,
+        )
+        self.assertQuerysetEqual(
+            d.django_group.user_set.all(),
+            ["d1", "d2"],
+            ordered=False,
+            transform=lambda u: u.username,
+        )
+
+    def test_removal(self):
+        """Test propagation of user removal."""
+
+        a = create_group("group_a", with_users=["a1", "a2"])
+        b = create_group("group_b", with_users=["b1", "b2"])
+        a.includes_groups.add(b)
+
+        self.assertQuerysetEqual(
+            a.django_group.user_set.all(),
+            ["a1", "a2", "b1", "b2"],
+            ordered=False,
+            transform=lambda u: u.username,
+        )
+
+        b.users.remove(User.objects.get(username="b1"))
+
+        self.assertQuerysetEqual(
+            a.django_group.user_set.all(),
+            ["a1", "a2", "b2"],
+            ordered=False,
+            transform=lambda u: u.username,
+        )
+        self.assertQuerysetEqual(
+            b.django_group.user_set.all(), ["b2"], transform=lambda u: u.username
+        )
+
+    def test_update(self):
+        """Test structure updates propagation."""
+
+        a = create_group("group_a")
+        b = create_group("group_b")
+        c = create_group("group_c")
+        a.includes_groups.add(b)
+        b.includes_groups.add(c)
+
+        # Update: set a's children to [c]
+        # Before update: a --> b --> c
+        # After update: b --> c <-- a
+        a.includes_groups.set([c])
+
+        self.assertQuerysetEqual(a.includes_groups.all(), [repr(c)])
+        self.assertQuerysetEqual(b.includes_groups.all(), [repr(c)])
+        self.assertQuerysetEqual(c.includes_groups.all(), [])
+
+
+class TestCycleDetection(TestCase):
+    """Test the cycle detection procedure."""
+
+    def test_loop(self):
+        """Test loops (a --> a) detection."""
+
+        a = create_group("group_a")
+
+        in_cycle = a.group_in_cycle(with_children=[a])
+        self.assertEqual(in_cycle, a)
+
+        in_cycle = a.group_in_cycle(with_children=[a, a, a])
+        self.assertEqual(in_cycle, a)
+
+    def test_trivial_cycle(self):
+        """Test trivial cycle detection (a --> b --> c --> a)."""
+
+        a = create_group("group_a")
+        b = create_group("group_b")
+        c = create_group("group_c")
+        a.includes_groups.add(b)
+        b.includes_groups.add(c)
+
+        in_cycle = c.group_in_cycle(with_children=[a])
+        self.assertIsNotNone(in_cycle)