How to test for raised exception in Python/Django?

Question

I've got a Django project in which I have a function which I want to test. Simplified, the function looks like this:

class InvalidUrlError(Exception):
    pass

def get_info_from_url(url):
    try:
        return url.split(':')[1].split('/')[0]
    except Exception:
        raise InvalidUrlError(f"Invalid url: {url}")

And my test looks like this:

class ToolsTestCase(TestCase):
    def test_get_info_from_url_wrong_formatted_url(self):
        self.assertRaises(InvalidUrlError, get_info_from_url("https://acc.images.data.ourcompany.com/"))

When I run it though, I get the following output:

$ ./manage.py test
Creating test database for alias 'default'...
System check identified no issues (0 silenced).
....E
======================================================================
ERROR: test_get_info_from_url_wrong_formatted_url (checker.tests.ToolsTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/kramer65/repos/auth-proxy/app/checker/tools.py", line 10, in get_info_from_url
    return url.split(':')[1].split('/')[0]
IndexError: list index out of range

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/kramer65/repos/auth-proxy/app/checker/tests.py", line 57, in test_get_info_from_url_wrong_formatted_url
    self.assertRaises(InvalidUrlError, get_info_from_url("https://acc.images.data.ourcompany.com/"))
  File "/home/kramer65/repos/auth-proxy/app/checker/tools.py", line 15, in get_info_from_url
    raise InvalidUrlError(f"Invalid url: {url}")
checker.tools.InvalidUrlError: Invalid url: https://acc.images.data.ourcompany.com/

----------------------------------------------------------------------
Ran 5 tests in 0.037s

FAILED (errors=1)
Destroying test database for alias 'default'...

Why does it raise the exceptions, instead of passing the tests? I think I do a comparable thing in another test, which works great.

Does anybody know what I'm doing wrong here?

Gasanov · Accepted Answer · 2019-12-19 14:09:12Z

7

You need to pass a callable instead of calling the function itself. Unittest docs for assertRaises

So change it to:

class ToolsTestCase(TestCase):
    def test_get_info_from_url_wrong_formatted_url(self):
        self.assertRaises(InvalidUrlError, get_info_from_url, "https://acc.images.data.ourcompany.com/")

Other option is to use assertRaises as context manager like this:

class ToolsTestCase(TestCase):
    def test_get_info_from_url_wrong_formatted_url(self):
        with self.assertRaises(InvalidUrlError):
            get_info_from_url("https://acc.images.data.ourcompany.com/")

edited Dec 19, 2019 at 14:09

answered Dec 19, 2019 at 14:01

Gasanov

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