Python Regexs Unit Testing

Question

I am trying to do some unit testing on a little regex def.

x = "TEST TEST TEST. Regular Expressions. TEST TEST TEST"

def find_start_end(phrase,sample_set):
    m = re.search(phrase, sample_set)

    start = m.start()
    end = m.end()
    return (start,end)
    #print(start,end)

if __name__ =="__main__":
    print(find_start_end("Regular Expressions", x))

This returns (16,35)....

My testing Unit is....

import unittest

class TestAlpha(unittest.TestCase):


def test_1(self):
    x = "Regular Expressions"
    self.assertEqual((0, 19), find_start_end("Regular Expressions", x))

def test_2(self):
        x = "TEST TEST TEST. Regular Expression. TEST TEST TEST"
        self.assertRaises(AttributeError, find_start_end("Regular Expressions", x))

if __name__ == "__main__":
    unittest.main()

Test 1 passes fine, my question is on test_2 how do I test for the AttributeError: 'NoneType' object has no attribute 'start'.

I was trying to use assertRaises, but I am not sure what I am doing wrong. I am open to any suggestions that would work better. Just trying to figure out how to test for the NoneType. I am very new to regular expressions.

falsetru · Accepted Answer · 2014-01-06 15:58:42Z

3

The code is using TestCase.assertRaises wrong way.

Replace following line:

self.assertRaises(AttributeError, find_start_end("Regular Expressions", x))

with:

# Do not call `find_start_end` directly,
#   but pass the function and its arguments to assertRaises
self.assertRaises(AttributeError, find_start_end, "Regular Expressions", x)

or:

# Use assertRaises as context manager
with self.assertRaises(AttributeError)
    find_start_end("Regular Expressions", x)

answered Jan 6, 2014 at 15:58

falsetru

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4 Comments

Trying_hard Over a year ago

ok that works Thanks. So in def assertRaises(self, excClass, callableObj=None, *args, **kwargs): "Regular Expressions" and x are my ** args?

falsetru Over a year ago

@Dumbkid_trying, Yes, they are. I added commented to the answer code.

Trying_hard Over a year ago

Thanks. That makes perfect sense now.

falsetru Over a year ago

@Dumbkid_trying, BTW, (m.start(), m.end()) could be expressed as m.span().

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