How to access error message from ValidationError?

Question

In my test.py I have:

with self.assertRaises(ValidationError):
    validate_zipfile(test_zip_path + '.zip')

And this works as intended. I also want to access the error message this ValidationError raises, so I can do this:

self.assertEqual(#error that I extract from the code above, 'Zip file not in correct format.')

Can you just write your own try-except here to check what you want? — shuttle87
– shuttle87, Commented Nov 12, 2015 at 17:06
@shuttle87: this is about unittesting, for which there is a handy framework to make assertions about exceptions being raised. — Martijn Pieters
– Martijn Pieters, Commented Nov 12, 2015 at 17:06
@MartijnPieters I see that it is. Previously I was using try-except with some assertions inside those because I didn't know you could store the context like you show in your answer. I'm going to go and change a couple of unit tests in my own code now to do this! — shuttle87
– shuttle87, Commented Nov 12, 2015 at 17:08

Martijn Pieters · Accepted Answer · 2018-09-28 11:16:25Z

6

Store the assertRaises() context manager, it has an exception attribute for you to introspect the exception raised:

with self.assertRaises(ValidationError) as exception_cm:
    validate_zipfile(test_zip_path + '.zip')

exception = exception_cm.exception
self.assertIn('Zip file not in correct format.', exception.messages)

You could use the Django-specific assertRaisesMessage() method, but take into account that that test does a simple substring test (e.g. you could potentially run into a false positive where you test for a substring of a longer message). Since ValidationError handles a list of messages, a test against ValidationError.messages is going to be more robust.

edited Sep 28, 2018 at 11:16

answered Nov 12, 2015 at 17:06

Martijn Pieters

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3 Comments

Saša Kalaba Over a year ago

Ty, simple and effective.

alias51 Over a year ago

How do you get the ValidationError.code from this method?

Martijn Pieters Over a year ago

@alias51 the exception attribute on the context manager is the exception instance. If you are expecting a ValidationError exception with a code attribute then that object should have the attribute: exception_cm.exception.code.

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