From c18cbc76e48b3b339a2b561df84417d4c83b458b Mon Sep 17 00:00:00 2001
From: Matt Westcott <matt@west.co.tt>
Date: Sun, 5 Feb 2017 18:22:51 +0000
Subject: [PATCH] Add tests for M2MFieldComparison

---
 wagtail/tests/testapp/models.py            |  1 +
 wagtail/wagtailadmin/tests/test_compare.py | 45 +++++++++++++++++++++-
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/wagtail/tests/testapp/models.py b/wagtail/tests/testapp/models.py
index bd2b46637b..4b972a6fe5 100644
--- a/wagtail/tests/testapp/models.py
+++ b/wagtail/tests/testapp/models.py
@@ -197,6 +197,7 @@ class EventPageSpeaker(Orderable, LinkFields):
     ]
 
 
+@python_2_unicode_compatible
 class EventCategory(models.Model):
     name = models.CharField("Name", max_length=255)
 
diff --git a/wagtail/wagtailadmin/tests/test_compare.py b/wagtail/wagtailadmin/tests/test_compare.py
index c2d5828651..a0f5bba8ec 100644
--- a/wagtail/wagtailadmin/tests/test_compare.py
+++ b/wagtail/wagtailadmin/tests/test_compare.py
@@ -7,7 +7,7 @@ from django.utils.functional import curry
 from django.utils.safestring import SafeText
 
 from wagtail.tests.testapp.models import (
-    EventPage, EventPageSpeaker, SimplePage, StreamPage, TaggedPage)
+    EventCategory, EventPage, EventPageSpeaker, SimplePage, StreamPage, TaggedPage)
 from wagtail.wagtailadmin import compare
 from wagtail.wagtailcore.blocks import StreamValue
 from wagtail.wagtailimages import get_image_model
@@ -255,6 +255,49 @@ class TestTagsFieldComparison(TestCase):
         self.assertTrue(comparison.has_changed())
 
 
+class TestM2MFieldComparison(TestCase):
+    fixtures = ['test.json']
+    comparison_class = compare.M2MFieldComparison
+
+    def setUp(self):
+        self.meetings_category = EventCategory.objects.create(name='Meetings')
+        self.parties_category = EventCategory.objects.create(name='Parties')
+        self.holidays_category = EventCategory.objects.create(name='Holidays')
+
+    def test_hasnt_changed(self):
+        christmas_event = EventPage.objects.get(url_path='/home/events/christmas/')
+        saint_patrick_event = EventPage.objects.get(url_path='/home/events/saint-patrick/')
+
+        christmas_event.categories = [self.meetings_category, self.parties_category]
+        saint_patrick_event.categories = [self.meetings_category, self.parties_category]
+
+        comparison = self.comparison_class(
+            EventPage._meta.get_field('categories'), christmas_event, saint_patrick_event
+        )
+
+        self.assertTrue(comparison.is_field)
+        self.assertFalse(comparison.is_child_relation)
+        self.assertEqual(comparison.field_label(), "Categories")
+        self.assertFalse(comparison.has_changed())
+        self.assertEqual(comparison.htmldiff(), 'Meetings, Parties')
+        self.assertIsInstance(comparison.htmldiff(), SafeText)
+
+    def test_has_changed(self):
+        christmas_event = EventPage.objects.get(url_path='/home/events/christmas/')
+        saint_patrick_event = EventPage.objects.get(url_path='/home/events/saint-patrick/')
+
+        christmas_event.categories = [self.meetings_category, self.parties_category]
+        saint_patrick_event.categories = [self.meetings_category, self.holidays_category]
+
+        comparison = self.comparison_class(
+            EventPage._meta.get_field('categories'), christmas_event, saint_patrick_event
+        )
+
+        self.assertTrue(comparison.has_changed())
+        self.assertEqual(comparison.htmldiff(), 'Meetings, <span class="deletion">Parties</span>, <span class="addition">Holidays</span>')
+        self.assertIsInstance(comparison.htmldiff(), SafeText)
+
+
 class TestForeignObjectComparison(TestCase):
     comparison_class = compare.ForeignObjectComparison