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Unit testing beginner question

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  Unit testing beginner question Andrius <andrius.a@gmail.com> - 2011-05-23 15:30 -0700
    Re: Unit testing beginner question Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-23 16:46 -0600
      Re: Unit testing beginner question Roy Smith <roy@panix.com> - 2011-05-23 20:19 -0400

#6099 — Unit testing beginner question

Hello,

would be gratefull for the explonation.

I did a simple test case:

def setUp(self):
  self.testListNone = None

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

and I am expecting test to pass, but I am getting exception:
Traceback (most recent call last):
    self.assertRaises(TypeError, self.testListNone[:1])
TypeError: 'NoneType' object is unsubscriptable

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

Ta,
Andrius

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#6101

On Mon, May 23, 2011 at 4:30 PM, Andrius <andrius.a@gmail.com> wrote:
> and I am expecting test to pass, but I am getting exception:
> Traceback (most recent call last):
>    self.assertRaises(TypeError, self.testListNone[:1])
> TypeError: 'NoneType' object is unsubscriptable
>
> I thought that assertRaises will pass since TypeError exception will
> be raised?

The second argument to assertRaises must be a function that
assertRaises will call.  assertRaises can't catch the error above
because it is raised when the argument is evaluated, before
assertRaises has even been called.

This would work:

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

Cheers,
Ian

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#6105

In article <mailman.1991.1306191316.9059.python-list@python.org>,
 Ian Kelly <ian.g.kelly@gmail.com> wrote:

> This would work:
> 
> self.assertRaises(TypeError, lambda: self.testListNone[:1])

If you're using the version of unittest from python 2.7, there's an even 
nicer way to write this:

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

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