Django/Python assertRaises with message check

Question

I am relatively new to Python and want to use a assertRaises test to check for a ValidationError, which works ok. However, I have many ValidationErrors and I want to make sure the right one is returned. I figured I could pass something into assertRaises but it doesn’t look like I can, so I figured I would just do an assertTrue and check the exception message. However, I don’t know how to access it. Is this even a good way to approach this issue? thanks.

class DailyEntriesTests(TestCase):
def test_cant_have_ip_and_user(self):
    u = createUser(False)
    de = createDailyEntry(u, "1.1.1.1", 1)
    with self.assertRaises(ValidationError) as cm:
        de.full_clean()

    # this line bombs - message doesn't exist. I also tried "error_code" like I saw in the documentation, but that doesn't work
    print(cm.exception.message)

    self.assertTrue(cm.exception.message.contains("Both"))

Asked By: skaz

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Source

Answer 1

You can just use assertRaisesRegexp.

with self.assertRaisesRegexp(ValidationError, "Both"):
    de.full_clean()

When you use it as a context manager the 2nd argument is a regular expression to search through the exception’s string representation.

Answered By: Louis

Answer 2

Nowadays you can use assertRaises as a context manager. This way you can capture the exception and inspect it later.

with self.assertRaises(SomeException) as cm:
    do_something()

the_exception = cm.exception
self.assertEqual(the_exception.error_code, 3)

Answered By: Christian Long

Answer 3

Since the question is related to Django, you could also use the assertRaisesMessage context manager when inheriting from django’s TestCase.

from django.test import TestCase

class ExceptionTest(TestCase):

    def test_call_raises_exception_with_custom_message(self):
        with self.assertRaisesMessage(Exception, 'My custom message!'):
            call_that_causes_exception()

Note: The assertRaisesMessage manager does an in lookup on the exceptions message: Say your exception raises "My custom message!", asserting for "custom message" passes. Bear this in mind especially if you have multiple (custom) exceptions with similar messages.

(E.g. two different exceptions raising "My custom message! Further details…" and "My custom message! No details." would both pass an assert for "My custom message!").

Answered By: Kim

Django/Python assertRaises with message check

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