Increased test coverage of django.utils.datastructures to 100%.

[ngnpope]

Supersedes #12442. I split out the tests for MultiValueDict and OrderedSet into two commits and added additional missing test coverage to these. Also in relation to MultiValueDict.update(), in that PR, Mads said:

I don't know how to trigger TypeError, and my attempts only triggered an AttributeError.

I came to the conclusion that it wasn't possible to trigger TypeError as the call to .items() was always going to trigger AttributeError for every other common type. Further, I noted that the behaviour of MultiValueDict.update() was inconsistent with and more strict than dict.update(). To my understanding, the main reason for overriding the .update() method is to a) ensure that the values are always lists, and b) special case to handle provision of another MultiValueDict instance.

So I added a commit that makes the behaviour as consistent with dict.update() as possible. A few exceptions are slightly differently worded due to the way dict.update() is implemented in C versus this Python implementation for MultiValueDict.update(), but they are comparable..

I've also attached a quick script I used to compare output of dict.update() and MultiValueDict.update() as we'll as before and after output:

Script to compare behaviour.

import sys
import traceback
from django.utils.datastructures import MultiValueDict

def test(values):
    for value in values:
        print(f'>>> dict().update({value!r})')
        try:
            result = dict().update(value)
        except Exception:
            traceback.print_exception(*sys.exc_info()[:-1], None)
        else:
            print(result)
    for value in values:
        print(f'>>> MultiValueDict().update({value!r})')
        try:
            result = MultiValueDict().update(value)
        except Exception:
            traceback.print_exception(*sys.exc_info()[:-1], None)
        else:
            print(result)

non_iterables = [None, True, False, 123, 123.45]
empty_iterables = ['', b'', (), [], set(), {}]
paired_iterables = [(('a', 1),), [('a', 1)], {('a', 1)}]
non_empty_iterables = ['123', b'123', (1, 2, 3), [1, 2, 3], {1, 2, 3}, {'a': 1}]

test(non_iterables)
test(empty_iterables)
test(paired_iterables)
test(non_empty_iterables)

Comparison before change in behavior.

>>> dict().update(None)
TypeError: 'NoneType' object is not iterable
>>> dict().update(True)
TypeError: 'bool' object is not iterable
>>> dict().update(False)
TypeError: 'bool' object is not iterable
>>> dict().update(123)
TypeError: 'int' object is not iterable
>>> dict().update(123.45)
TypeError: 'float' object is not iterable
>>> MultiValueDict().update(None)
AttributeError: 'NoneType' object has no attribute 'items'
>>> MultiValueDict().update(True)
AttributeError: 'bool' object has no attribute 'items'
>>> MultiValueDict().update(False)
AttributeError: 'bool' object has no attribute 'items'
>>> MultiValueDict().update(123)
AttributeError: 'int' object has no attribute 'items'
>>> MultiValueDict().update(123.45)
AttributeError: 'float' object has no attribute 'items'
>>> dict().update('')
None
>>> dict().update(b'')
None
>>> dict().update(())
None
>>> dict().update([])
None
>>> dict().update(set())
None
>>> dict().update({})
None
>>> MultiValueDict().update('')
AttributeError: 'str' object has no attribute 'items'
>>> MultiValueDict().update(b'')
AttributeError: 'bytes' object has no attribute 'items'
>>> MultiValueDict().update(())
AttributeError: 'tuple' object has no attribute 'items'
>>> MultiValueDict().update([])
AttributeError: 'list' object has no attribute 'items'
>>> MultiValueDict().update(set())
AttributeError: 'set' object has no attribute 'items'
>>> MultiValueDict().update({})
None
>>> dict().update((('a', 1),))
None
>>> dict().update([('a', 1)])
None
>>> dict().update({('a', 1)})
None
>>> MultiValueDict().update((('a', 1),))
AttributeError: 'tuple' object has no attribute 'items'
>>> MultiValueDict().update([('a', 1)])
AttributeError: 'list' object has no attribute 'items'
>>> MultiValueDict().update({('a', 1)})
AttributeError: 'set' object has no attribute 'items'
>>> dict().update('123')
ValueError: dictionary update sequence element #0 has length 1; 2 is required
>>> dict().update(b'123')
TypeError: cannot convert dictionary update sequence element #0 to a sequence
>>> dict().update((1, 2, 3))
TypeError: cannot convert dictionary update sequence element #0 to a sequence
>>> dict().update([1, 2, 3])
TypeError: cannot convert dictionary update sequence element #0 to a sequence
>>> dict().update({1, 2, 3})
TypeError: cannot convert dictionary update sequence element #0 to a sequence
>>> dict().update({'a': 1})
None
>>> MultiValueDict().update('123')
AttributeError: 'str' object has no attribute 'items'
>>> MultiValueDict().update(b'123')
AttributeError: 'bytes' object has no attribute 'items'
>>> MultiValueDict().update((1, 2, 3))
AttributeError: 'tuple' object has no attribute 'items'
>>> MultiValueDict().update([1, 2, 3])
AttributeError: 'list' object has no attribute 'items'
>>> MultiValueDict().update({1, 2, 3})
AttributeError: 'set' object has no attribute 'items'
>>> MultiValueDict().update({'a': 1})
None

Comparison after change in behavior.

>>> dict().update(None)
TypeError: 'NoneType' object is not iterable
>>> dict().update(True)
TypeError: 'bool' object is not iterable
>>> dict().update(False)
TypeError: 'bool' object is not iterable
>>> dict().update(123)
TypeError: 'int' object is not iterable
>>> dict().update(123.45)
TypeError: 'float' object is not iterable
>>> MultiValueDict().update(None)
TypeError: 'NoneType' object is not iterable
>>> MultiValueDict().update(True)
TypeError: 'bool' object is not iterable
>>> MultiValueDict().update(False)
TypeError: 'bool' object is not iterable
>>> MultiValueDict().update(123)
TypeError: 'int' object is not iterable
>>> MultiValueDict().update(123.45)
TypeError: 'float' object is not iterable
>>> dict().update('')
None
>>> dict().update(b'')
None
>>> dict().update(())
None
>>> dict().update([])
None
>>> dict().update(set())
None
>>> dict().update({})
None
>>> MultiValueDict().update('')
None
>>> MultiValueDict().update(b'')
None
>>> MultiValueDict().update(())
None
>>> MultiValueDict().update([])
None
>>> MultiValueDict().update(set())
None
>>> MultiValueDict().update({})
None
>>> dict().update((('a', 1),))
None
>>> dict().update([('a', 1)])
None
>>> dict().update({('a', 1)})
None
>>> MultiValueDict().update((('a', 1),))
None
>>> MultiValueDict().update([('a', 1)])
None
>>> MultiValueDict().update({('a', 1)})
None
>>> dict().update('123')
ValueError: dictionary update sequence element #0 has length 1; 2 is required
>>> dict().update(b'123')
TypeError: cannot convert dictionary update sequence element #0 to a sequence
>>> dict().update((1, 2, 3))
TypeError: cannot convert dictionary update sequence element #0 to a sequence
>>> dict().update([1, 2, 3])
TypeError: cannot convert dictionary update sequence element #0 to a sequence
>>> dict().update({1, 2, 3})
TypeError: cannot convert dictionary update sequence element #0 to a sequence
>>> dict().update({'a': 1})
None
>>> MultiValueDict().update('123')
ValueError: not enough values to unpack (expected 2, got 1)
>>> MultiValueDict().update(b'123')
TypeError: cannot unpack non-iterable int object
>>> MultiValueDict().update((1, 2, 3))
TypeError: cannot unpack non-iterable int object
>>> MultiValueDict().update([1, 2, 3])
TypeError: cannot unpack non-iterable int object
>>> MultiValueDict().update({1, 2, 3})
TypeError: cannot unpack non-iterable int object
>>> MultiValueDict().update({'a': 1})
None

Finally, there is an extra commit that removes support for providing an instance of Exception to the warning argument for ImmutableList. This is untested, undocumented and unused in Django itself. It didn't seem worth adding a test and preserving this behavior.

[carltongibson]

Thanks for this @pope1ni. Looks good at first glance. Let me just give it a ponder. (Will respond fully for next week.)

[carltongibson]

Hey @pope1ni. I think this is great. 👍

The 4 main commits make sense separately I think.

[felixxm]

@pope1ni Thanks 👍 just some nitpicks

[felixxm]

@pope1ni Thanks👍

"Removed..." in the third commit😉

[ngnpope]

"Removed..." in the third commit

Auuugh! 🙀 😂

[ngnpope]

I'm really being mocked now: Test failure in cache.tests.PyMemcacheCacheTests.test_touch. 😂