Fixed #19890 -- ifchanged templatetag rendered its content twice

The content of ifchanged template tag was rendered twice: first time, to
compare it with the previous value and the second time, to return the
rendered output.

1 files changed, 12 insertions, 0 deletions

diff --git a/tests/regressiontests/templates/tests.py b/tests/regressiontests/templates/tests.py
index 28d85cae9d..e1e448acba 100644
--- a/tests/regressiontests/templates/tests.py
+++ b/tests/regressiontests/templates/tests.py
@@ -441,6 +441,18 @@ class Templates(TestCase):
         output1 = template.render(Context({'foo': range(3), 'get_value': lambda: next(gen1)}))
         self.assertEqual(output1, '[0,1,2,3]', 'Expected [0,1,2,3] in first template, got {0}'.format(output1))
 
+    def test_ifchanged_render_once(self):
+        """ Test for ticket #19890. The content of ifchanged template tag was
+        rendered twice."""
+
+        template = Template('{% ifchanged %}{{ gen.next }}{% endifchanged %}')
+        def gen():
+            for i in xrange(1,10):
+                yield 'iteration no %d' % i
+
+        output = template.render(Context({'gen': gen()}))
+        self.assertEqual(output, 'iteration no 1')
+
     def test_templates(self):
         template_tests = self.get_template_tests()
         filter_tests = filters.get_filter_tests()