Test if ValidationError was raised

Question

I want to test if an exception was raised how can I do that?

in my models.py I have this function, the one I want to test:

  def validate_percent(value):
    if not (value >= 0 and value <= 100):
      raise ValidationError('error')

in my tests.py I tried this:

def test_validate_percent(self):
    self.assertRaises(ValidationError, validate_percent(1000))

the output of the test is:

..E
======================================================================
ERROR: test_validate_percent (tm.tests.models.helpers.HelpersTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/...py", line 21, in test_validate_percent
    self.assertRaises(ValidationError, validate_percent(1000))
  File "/....py", line 25, in validate_percent
    raise ValidationError(u'error' % value)
ValidationError: ['error']

Note that in Python your validation check should be written `if not 0 <= value <= 100`. — Daniel Roseman, Apr 25 '13 at 12:57

score 28 · Accepted Answer · answered Apr 25 '13 at 12:33

28

assertRaises is used as a context manager:

def test_validate_percent(self):
    with self.assertRaises(ValidationError):
        validate_percent(1000)

or with a callable:

def test_validate_percent(self):
    self.assertRaises(ValidationError, validate_percent, 1000)

http://docs.python.org/2/library/unittest.html#unittest.TestCase.assertRaises

answered Apr 25 '13 at 12:33

Pavel Anossov

60,842
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1

Using assertRaises as a context manager was added in Python 2.7, so it's not available on Python 2.6 or older - such as when using the system installed Python on CentOS 5.x. This bit me integrating unittests into the RPM build process on CentOS 5.7. – pcurry Apr 25 '13 at 13:22
unbelievable :) – Tolgahan ÜZÜN Feb 20 '18 at 08:41
In my case had to use the [context manager](https://stackoverflow.com/a/3166985/5675325). – Tiago Martins Peres Oct 03 '22 at 12:57

score 3 · Answer 2 · answered Apr 25 '13 at 12:34

3

def test_validate_percent(self):
    self.assertRaises(ValidationError, validate_percent, 1000)

answered Apr 25 '13 at 12:34

waitingkuo

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Test if ValidationError was raised

2 Answers2