How to test custom template tags in Django?

I'm adding a set of template tags to a Django application and I'm not sure how to test them. I've used them in my templates and they seem to be working but I was looking for something more formal. The main logic is done in the models/model managers and has been tested. The tags simply retrieve data and store it in a context variable such as

{% views_for_object widget as views %}
"""
Retrieves the number of views and stores them in a context variable.
"""
# or
{% most_viewed_for_model main.model_name as viewed_models %}
"""
Retrieves the ViewTrackers for the most viewed instances of the given model.
"""

So my question is do you typically test your template tags and if you do开发者_如何学编程 how do you do it?

This is a short passage of one of my test files, where self.render_template a simple helper method in the TestCase is:

    rendered = self.render_template(
        '{% load templatequery %}'
        '{% displayquery django_templatequery.KeyValue all() with "list.html" %}'
    )
    self.assertEqual(rendered,"foo=0\nbar=50\nspam=100\negg=200\n")

    self.assertRaises(
        template.TemplateSyntaxError,
        self.render_template,
        '{% load templatequery %}'
        '{% displayquery django_templatequery.KeyValue all() notwith "list.html" %}'
    )

It is very basic and uses blackbox testing. It just takes a string as template source, renders it and checks if the output equals the expected string.

The render_template method is quite simplistic:

from django.template import Context, Template

class MyTest(TestCase):
    def render_template(self, string, context=None):
        context = context or {}
        context = Context(context)
        return Template(string).render(context)

You guys got me on the right track. It's possible to check that the context was correctly changed after the render:

class TemplateTagsTestCase(unittest.TestCase):        
    def setUp(self):    
        self.obj = TestObject.objects.create(title='Obj a')

    def testViewsForOjbect(self):
        ViewTracker.add_view_for(self.obj)
        t = Template('{% load my_tags %}{% views_for_object obj as views %}')
        c = Context({"obj": self.obj})
        t.render(c)
        self.assertEqual(c['views'], 1)

A good example of how to test template tags test of flatpage templatetags

Strings can be rendered as templates, so you could write a test that includes a simple 'template' using your templatetag as a string and just make sure it renders correctly given a certain context.

When I was testing my template tags, I would have the tag, itself, return a string containing the text or dict I was working with ... sort of along the lines of the other suggestion.

Since tags can modify the context and/or return a string to be rendered -- I found it was fastest just to view the rendered string.

Instead of:

return ''

Have it:

return str(my_data_that_I_am_testing)

Until you are happy.