1、前言#####
最近在学习django，使用的书是《Python Web开发 测试驱动方法》，在第四章中遇到了一个问题使用render_to_string()函数。学习过程中使用的是py2，Django的版本是1.10.1。
2、问题描述#####
第四章的单元测试部分代码：
class HomePageTest(TestCase):
[...]
def test_home_page_returns_correct_html(self):
request = HttpRequest()
response = home_page(request)
expected_html = render_to_string('home.html'）
self.assertEqual(response.content.decode(), expected_html)
[...]
在没有在表单中加入CSRF令牌{% csrf_token %}时，运行都是正常的。
I:\Django_learn\superlists>python manage.py test
Creating test database for alias 'default'...
...
----------------------------------------------------------------------
Ran 3 tests in 0.000s
OK
Destroying test database for alias 'default'...
I:\Django_learn\superlists>
现在在home.html中加入CSRF令牌{% csrf_token %}后。
<html>
<head>
<title>To-Do lists</title>
</head>
<body>
<h1>Your To-Do lists</h1>
<form method="POST">
<input name="item_text" id="id_new_item" placeholder="Enter a to-do item"/>
{% csrf_token %}
</form>
<table id="id_list_table">
<tr><td>{{ new_item_text }}</td></tr>
</table>
</body>
</html>
再次运行单元测试
I:\Django_learn\superlists>python manage.py test
Creating test database for alias 'default'...
.F.
======================================================================
FAIL: test_home_page_returns_correct_html (lists.tests.HomePageTest)
----------------------------------------------------------------------
Traceback (most recent call last):
File "I:\Django_learn\superlists\lists\tests.py", line 28, in test_home_page_returns_correct_html
self.assertEqual(response.content.decode(), expected_html)
AssertionError: u'<html>\n<head>\n <title>To-Do lists</title>\n</head>\n<body>\n <h1>Your To-Do lists</h1>\n <form method="POST">\n <input name="item_text" id="id_new_item" placeholder="Enter a to-do item"/>\n <input type=\'hidden\' name=\'csrfmiddlewaretoken\' value=\'WkE5AMVHQu5oVmJ6wFSU2KjMvXV6yGYwsB3IJ0Too0QM4xXKVPj6BJ24DBLP600v\' />\n </form>\n <table id="id_list_table">\n <tr><td></td></tr>\n </table>\n</body>\n</html>\n' != u'<html>\n<head>\n <title>To-Do lists</title>\n</head>\n<body>\n <h1>Your To-Do lists</h1>\n <form method="POST">\n <input name="item_text" id="id_new_item" placeholder="Enter a to-do item"/>\n \n </form>\n <table id="id_list_table">\n <tr><td></td></tr>\n </table>\n</body>\n</html>\n'
----------------------------------------------------------------------
Ran 3 tests in 0.047s
FAILED (failures=1)
Destroying test database for alias 'default'...
根据错误信息可以知道在最后的断言self.assertEqual(response.content.decode(), expected_html)导致测试失败。
我们添加两行用于调试，打印出response.content.decode()和expected_html.
print 'response.content.decode()\n', response.content.decode()
print 'expected_html\n', expected_html
I:\Django_learn\superlists>python manage.py test
Creating test database for alias 'default'...
.response.content.decode()
<html>
<head>
<title>To-Do lists</title>
</head>
<body>
<h1>Your To-Do lists</h1>
<form method="POST">
<input name="item_text" id="id_new_item" placeholder="Enter a to-do item"/>
<input type='hidden' name='csrfmiddlewaretoken' value='VUMXA6dNnUT8Y2rAY3nAcQyTMtJKGznXqts0HbPaDWN16b4uiMDkFMWp1EVbC3xu' />
</form>
<table id="id_list_table">
<tr><td></td></tr>
</table>
</body>
</html>
expected_html
<html>
<head>
<title>To-Do lists</title>
</head>
<body>
<h1>Your To-Do lists</h1>
<form method="POST">
<input name="item_text" id="id_new_item" placeholder="Enter a to-do item"/>
</form>
<table id="id_list_table">
<tr><td></td></tr>
</table>
</body>
</html>
..
----------------------------------------------------------------------
Ran 3 tests in 0.031s
OK
Destroying test database for alias 'default'...
I:\Django_learn\superlists>
在渲染模板时，Django 会把这个模板标签替换成一个<input type="hidden">元素,其值是CSRF 令牌。
从上面的html代码可以看出，通过视图函数home_page()渲染得到的响应包含csrf转换的<input>元素，而render_to_string()则未生成该部分，所以导致测试失败。
3、如何解决#####
经过google，在stackoverflow找到了解决办法。
按照stackoverflow上的解决办法(当前djano==1.10.1)，我使用expected_html = render_to_string('home.html', request=request)和render_to_string('index.html', context_instance=RequestContext(request))仍然会报错，于是将自己django版本降低到1.8后使用expected_html = render_to_string('home.html', request=request)，测试通过。
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