blocks|key|3178094|text|使用assertRaises的常用方法是调用一个函数：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3178095|self.assertRaises(TypeError,+test_function,+args)|code-block|syntax|javascript|3178096|为了测试函数调用test_function(args)是否会引发TypeError。|3178097|self.testListNone[:1]的问题在于，在调用assertRaises方法之前，Python会立即计算表达式。将test_function和args作为单独的参数传递给self.assertRaises的全部原因是允许assertRaises从try...except块中调用test_function(args)，从而允许assertRaises捕获异常。|3178098|由于您已经定义了self.testListNone+=+None，并且需要调用一个函数，因此可以按如下方式使用operator.itemgetter：|3178099|import+operator
self.assertRaises(TypeError,+operator.itemgetter,+(self.testListNone,slice(None,1)))|3178100|因为|3178101|operator.itemgetter(self.testListNone,slice(None,1))|3178102|是self.testListNone[:1]的一种冗长的说法，但它将函数(operator.itemgetter)与参数分开。|3178103|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/library/operator.html#operator.itemgetter^0|2|C|0|0|0|0|L|U|C|1R|D|25|4|2J|H|38|C|3L|C|41|J|4P|C|0|8|O|1J|J|0|0|0|0|0|1|L|11|J|0^^$0|@$1|2|3|4|5|6|7|16|8|@$9|17|A|18|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|19|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1A|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|1B|8|@$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]|$9|1K|A|1L|B|C]|$9|1M|A|1N|B|C]|$9|1O|A|1P|B|C]|$9|1Q|A|1R|B|C]|$9|1S|A|1T|B|C]]|D|@]|E|$]]|$1|O|3|P|5|6|7|1U|8|@$9|1V|A|1W|B|C]]|D|@$9|1X|A|1Y|1|1Z]]|E|$]]|$1|Q|3|R|5|H|7|20|8|@]|D|@]|E|$I|J]]|$1|S|3|T|5|6|7|21|8|@]|D|@]|E|$]]|$1|U|3|V|5|H|7|22|8|@]|D|@]|E|$I|J]]|$1|W|3|X|5|6|7|23|8|@$9|24|A|25|B|C]|$9|26|A|27|B|C]]|D|@]|E|$]]|$1|Y|3|-4|5|6|7|28|8|@]|D|@]|E|$]]]|Z|$10|$5|11|12|13|E|$14|15]]]]

The usual way to use <code>assertRaises</code> is to call a function:

<pre><code>self.assertRaises(TypeError, test_function, args)
</code></pre>

to test that the function call test_function(args) raises a TypeError.

The problem with <code>self.testListNone[:1]</code> is that Python evaluates the expression immediately, before the <code>assertRaises</code> method is called. The whole reason why <code>test_function</code> and <code>args</code> is passed as separate arguments to <code>self.assertRaises</code> is to allow <code>assertRaises</code> to call <code>test_function(args)</code> from within a <code>try...except</code> block, allowing <code>assertRaises</code> to catch the exception.

Since you've defined <code>self.testListNone = None</code>, and you need a function to call, you might use <a href="http://docs.python.org/library/operator.html#operator.itemgetter">operator.itemgetter</a> like this:

<pre><code>import operator
self.assertRaises(TypeError, operator.itemgetter, (self.testListNone,slice(None,1)))
</code></pre>

since 

<pre><code>operator.itemgetter(self.testListNone,slice(None,1))
</code></pre>

is a long-winded way of saying <code>self.testListNone[:1]</code>, but which separates the function (<code>operator.itemgetter</code>) from the arguments.

blocks|key|267634|text|问题是在调用assertRaises之前会引发TypeError，因为在调用方法之前需要计算assertRaises的参数。您需要传递一个lambda表达式，如下所示：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|267635|self.assertRaises(TypeError,+lambda:+self.testListNone[:1])|code-block|syntax|javascript|267636|entityMap^0|6|C|N|9|1A|C|1X|6|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|L|$]]

The problem is the <code>TypeError</code> gets raised 'before' <code>assertRaises</code> gets called since the arguments to <code>assertRaises</code> need to be evaluated before the method can be called. You need to pass a <code>lambda</code> expression like:

<pre><code>self.assertRaises(TypeError, lambda: self.testListNone[:1])
</code></pre>

blocks|key|269130|text|如果您使用的是python2.7或更高版本，则可以使用assertRaises的功能作为上下文管理器，并执行以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|269131|with+self.assertRaises(TypeError):
++++self.testListNone[:1]|code-block|syntax|javascript|269132|如果你正在使用python2.6，除了之前给出的方法之外，另一种方法是使用unittest2，它是python2.6的一个单元测试新特性的后端，你可以使用上面的代码来使它工作。|269133|注意:我是新特性(SkipTest，测试发现...)的铁杆粉丝。所以我打算尽可能多地使用unittest2。我建议做同样的事情，因为在python2.6+<中有比unittest更多的东西。|269134|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/library/unittest.html#unittest.TestCase.assertRaises|1|http://pypi.python.org/pypi/unittest2/0.5.1^0|R|C|0|0|0|11|9|1|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|11|8|@]|9|@$A|12|B|13|1|14]]|C|$]]|$1|K|3|L|5|6|7|15|8|@]|9|@]|C|$]]|$1|M|3|-4|5|6|7|16|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]]]

If you are using python2.7 or above you can use the ability of <a href="http://docs.python.org/library/unittest.html#unittest.TestCase.assertRaises">assertRaises</a> to be use as a context manager and do:

<pre><code>with self.assertRaises(TypeError):
 self.testListNone[:1]
</code></pre>

If you are using python2.6 another way beside the one given until now is to use <a href="http://pypi.python.org/pypi/unittest2/0.5.1">unittest2</a> which is a back port of unittest new feature to python2.6, and you can make it work using the code above.

N.B: I'm a big fan of the new feature (SkipTest, test discovery ...) of unittest so I intend to use unittest2 as much as I can. I advise to do the same because there is a lot more than what unittest come with in python2.6 &lt;.

blocks|key|2964408|text|完整的代码片段如下所示。它将@mouad的答案扩展为对错误消息(或其args的str表示)进行断言，这可能会很有用。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2964409|from+unittest+import+TestCase


class+TestNoneTypeError(TestCase):

++def+setUp(self):+
++++self.testListNone+=+None

++def+testListSlicing(self):
++++with+self.assertRaises(TypeError)+as+ctx:
++++++++self.testListNone[:1]
++++self.assertEqual("'NoneType'+object+is+not+subscriptable",+str(ctx.exception))|code-block|syntax|javascript|2964410|entityMap^0|Y|4|13|3|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

Complete snippet would look like the following. It expands @mouad's answer to asserting on error's message (or generally <code>str</code> representation of its <code>args</code>), which may be useful.

<pre><code>from unittest import TestCase


class TestNoneTypeError(TestCase):

 def setUp(self): 
 self.testListNone = None

 def testListSlicing(self):
 with self.assertRaises(TypeError) as ctx:
 self.testListNone[:1]
 self.assertEqual("'NoneType' object is not subscriptable", str(ctx.exception))
</code></pre>

I did a simple test case:

<pre><code>def setUp(self):

 self.testListNone = None

def testListSlicing(self):

 self.assertRaises(TypeError, self.testListNone[:1])
</code></pre>

and I am expecting test to pass, but I am getting exception:

<pre><code>Traceback (most recent call last):

 self.assertRaises(TypeError, self.testListNone[:1])

TypeError: 'NoneType' object is unsubscriptable
</code></pre>

I thought that assertRaises will pass since TypeError exception will
be raised?

How to properly use unit-testing's assertRaises() with NoneType objects?

单元测试

Python

我做了一个简单的测试用例：def setUp(self):  self.testListNone = Nonedef testListSlicing(self):  self.assertRaises(TypeError, self.testListNone[:1])我希望测试能通过，但是我得到了异常：Tracebac...

问如何在NoneType对象中正确使用单元测试的assertRaises()？
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问如何在NoneType对象中正确使用单元测试的assertRaises()？
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