Python/Django: how to assert that unit test result contains a certain string?

Question

In a python unit test (actually Django), what is the correct assert statement that will tell me if my test result contains a string of my choosing?

self.assertContainsTheString(result, {"car" : ["toyota","honda"]})

I want to make sure that my result contains at least the json object (or string) that I specified as the second argument above

{"car" : ["toyota","honda"]}

Asked By: user798719

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Source

Answer 1

Build a JSON object using json.dumps().

Then compare them using assertEqual(result, your_json_dict)

import json

expected_dict = {"car":["toyota", "honda"]}
expected_dict_json = json.dumps(expected_dict)

self.assertEqual(result, expected_dict_json)

Answered By: Vincent Audebert

Answer 2

self.assertContains(result, "abcd")

You can modify it to work with json.

Use self.assertContains only for HttpResponse objects. For other objects, use self.assertIn.

Answered By: Akshar Raaj

Answer 3

You can write assertion about expected part of string in another string with a simple assertTrue + in python keyword :

self.assertTrue("expected_part_of_string" in my_longer_string)

Answered By: Pierre Criulanscy

Answer 4

To assert if a string is or is not a substring of another, you should use assertIn and assertNotIn:

# Passes
self.assertIn('bcd', 'abcde')

# AssertionError: 'bcd' unexpectedly found in 'abcde'
self.assertNotIn('bcd', 'abcde')

These are new since Python 2.7 and Python 3.1

Answered By: Ed I

Answer 5

As mentioned by Ed I, assertIn is probably the simplest answer to finding one string in another. However, the question states:

I want to make sure that my result contains at least the json object (or string) that I specified as the second argument above,i.e., {"car" : ["toyota","honda"]}

Therefore I would use multiple assertions so that helpful messages are received on failure – tests will have to be understood and maintained in the future, potentially by someone that didn’t write them originally. Therefore assuming we’re inside a django.test.TestCase:

# Check that `car` is a key in `result`
self.assertIn('car', result)
# Compare the `car` to what's expected (assuming that order matters)
self.assertEqual(result['car'], ['toyota', 'honda'])

Which gives helpful messages as follows:

# If 'car' isn't in the result:
AssertionError: 'car' not found in {'context': ..., 'etc':... }
# If 'car' entry doesn't match:
AssertionError: Lists differ: ['toyota', 'honda'] != ['honda', 'volvo']

First differing element 0:
toyota
honda

- ['toyota', 'honda']
+ ['honda', 'volvo']

Answered By: jamesc

Python/Django: how to assert that unit test result contains a certain string?

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