diff --git a/conntrackt/tests/test_forms.py b/conntrackt/tests/test_forms.py
--- a/conntrackt/tests/test_forms.py
+++ b/conntrackt/tests/test_forms.py
@@ -1,23 +1,107 @@
 # Django imports.
 from django.test import TestCase
 
+# Python third-party library imports.
+import mock
+
 # Application imports.
-from conntrackt.forms import EntityForm
+from conntrackt.forms import WidgetCSSClassFormMixin, PlaceholderFormMixin
+from conntrackt.forms import EntityForm, InterfaceForm, CommunicationForm
+
+# Test imports.
+from .forms import FormWithWidgetCSSClassFormMixin, FormWithPlaceholderFormMixin
 
 
-class EntityFormTest(TestCase):
+class WidgetCSSClassFormMixinTest(TestCase):
     """
-    Tests for the custom Entity model form.
+    Tests the form mixin.
     """
 
-    def test_styling(self):
+    def test_apply_to_all(self):
+        """
+        Test if CSS class is appled to all form field widgets.
+        """
+
+        # Set-up the form.
+        form_class = FormWithWidgetCSSClassFormMixin
+        form_class.widget_css_classes = {"ALL": "test"}
+        form = form_class()
+
+        self.assertEqual(form.fields["field1"].widget.attrs["class"], "test")
+        self.assertEqual(form.fields["field2"].widget.attrs["class"], "test")
+
+    def test_apply_to_single(self):
         """
-        Test that the form styling is set-up correctly.
+        Test if CSS class is appled to a single field widget.
+        """
+
+        # Set-up the form.
+        form_class = FormWithWidgetCSSClassFormMixin
+        form_class.widget_css_classes = {"field2": "test"}
+        form = form_class()
+
+        self.assertEqual(form.fields["field1"].widget.attrs.get("class", None), None)
+        self.assertEqual(form.fields["field2"].widget.attrs["class"], "test")
+
+    def test_apply_multiple(self):
+        """
+        Tests if different class is applied to multiple form field widgets.
         """
 
-        form = EntityForm()
+        # Set-up the form.
+        form_class = FormWithWidgetCSSClassFormMixin
+        form_class.widget_css_classes = {"field1": "f1",
+                                         "field2": "f2"}
+        form = form_class()
+
+        self.assertEqual(form.fields["field1"].widget.attrs["class"], "f1")
+        self.assertEqual(form.fields["field2"].widget.attrs["class"], "f2")
+
+    def test_apply_to_all_additional(self):
+        """
+        Tests if all widgets get the same CSS class in addition to induvidual
+        ones.
+        """
+
+        # Set-up the form.
+        form_class = FormWithWidgetCSSClassFormMixin
+        form_class.widget_css_classes = {"field1": "f1",
+                                         "field2": "f2",
+                                         "ALL": "all"}
+        form = form_class()
+
+        self.assertEqual(sorted(["f1", "all"]), sorted(form.fields["field1"].widget.attrs["class"].split(" ")))
+        self.assertEqual(sorted(["f2", "all"]), sorted(form.fields["field2"].widget.attrs["class"].split(" ")))
+
 
-        self.assertIn("span6", form.fields["name"].widget.attrs["class"])
-        self.assertIn("span6", form.fields["description"].widget.attrs["class"])
-        self.assertIn("span6", form.fields["project"].widget.attrs["class"])
-        self.assertIn("span6", form.fields["location"].widget.attrs["class"])
+class PlaceholderFormMixinTest(TestCase):
+    """
+    Tests the form mixin.
+    """
+
+    def test_apply_one(self):
+        """
+        Test if a single placeholder is applied to a form field widget.
+        """
+
+        # Set-up the form.
+        form_class = FormWithPlaceholderFormMixin
+        form_class.widget_placeholders = {"field1": "place1"}
+        form = form_class()
+
+        self.assertEqual(form.fields["field1"].widget.attrs["placeholder"], "place1")
+        self.assertEqual(form.fields["field2"].widget.attrs.get("placeholder", None), None)
+
+    def test_apply_multiple(self):
+        """
+        Test if multiple placeholders are applied to form field widgets.
+        """
+
+        # Set-up the form.
+        form_class = FormWithPlaceholderFormMixin
+        form_class.widget_placeholders = {"field1": "place1",
+                                   "field2": "place2"}
+        form = form_class()
+
+        self.assertEqual(form.fields["field1"].widget.attrs["placeholder"], "place1")
+        self.assertEqual(form.fields["field2"].widget.attrs["placeholder"], "place2")