如何为此Django自定义标签编写测试用例

Question

• Django version : v1.10
• Python : 3.5 (this is important as it turns out .. look at the answer)

I found this answer in order to have a if-else tag to compare the request.path in Django templates

https://stackoverflow.com/a/19895344/80353

from django import template
from django.template.base import Node, NodeList, TemplateSyntaxError

register = template.Library()

class IfCurrentViewNode(Node):
    child_nodelists = ('nodelist_true', 'nodelist_false')

    def __init__(self, view_name, nodelist_true, nodelist_false):
        self.view_name = view_name
        self.nodelist_true, self.nodelist_false = nodelist_true, nodelist_false

    def __repr__(self):
        return "<IfCurrentViewNode>"

    def render(self, context):
        view_name = self.view_name.resolve(context, True)
        request = context['request']
        if request.resolver_match.url_name == view_name:
            return self.nodelist_true.render(context)
        return self.nodelist_false.render(context)


def do_ifcurrentview(parser, token):
    bits = token.split_contents()
    if len(bits) < 2:
        raise TemplateSyntaxError("'%s' takes at least one argument"
                                  " (path to a view)" % bits[0])
    view_name = parser.compile_filter(bits[1])
    nodelist_true = parser.parse(('else', 'endifcurrentview'))
    token = parser.next_token()
    if token.contents == 'else':
        nodelist_false = parser.parse(('endifcurrentview',))
        parser.delete_first_token()
    else:
        nodelist_false = NodeList()
    return IfCurrentViewNode(view_name, nodelist_true, nodelist_false)

@register.tag
def ifcurrentview(parser, token):
    """
    Outputs the contents of the block if the current view match the argument.

    Examples::

        {% ifcurrentview 'path.to.some_view' %}
            ...
        {% endifcurrentview %}

        {% ifcurrentview 'path.to.some_view' %}
            ...
        {% else %}
            ...
        {% endifcurrentview %}
    """
    return do_ifcurrentview(parser, token)

Was wondering if there's a way to write test case to cover this custom code?

I want to maintain our test coverage percentage

Answer 1

You should be able to cover most, if not all of that using mock. For example, let's say you want to test the render function:

from unittest.mock import Mock

def test_render_url_match(self):
    mock_request = Mock()
    matching_url_name = 'url_name'
    mock_nodelist_true, mock_nodelist_false = Mock(), Mock()
    mock_view_name = Mock()
    mock_view_name.resolve.return_value = matching_url_name
    mock_request.resolver_match.url_name = matching_url_name
    mock_context = {'request': mock_request}

    custom_node = IfCurrentViewNode(mock_view_name, mock_nodelist_true, mock_nodelist_false)
    custom_node.render(mock_context)

    # You can then test that the correct function was called:
    # you can change to `assert_called_once` if using Python 3.6
    mock_nodelist_true.render.assert_called_once_with(mock_context)

By setting up the mocks that way, I've ensured that this request.resolver_match.url_name == view_name will be true, and hit this line: return self.nodelist_true.render(context) . You can then set up the url name so they don't match and cover the false case.

Then, for the do_ifcurrentview function, you can mock out whatever pieces you need to as well. Maybe you don't want to mess with getting parser.compile_filter to return what you need. Just mock it and change the return value:

with mock.patch('parser.compile_filter') as mock_compile_filter:
    mock_compile_filter.return_value = 'my_expected_view_name'