pystubs 2018.5.3

Dummy values for equality testing

PyStubs: dummy values for equality testing

This tiny Python module provides various types that can be used to check for conditions using equality (==) testing. For example, to test whether a number is less than 5:

>>> from stubs import *
>>> 2 == LessThan(5)
True

Which is completely equivalent to:

>>> 2 < 5
True

This approach comes in handy when comparing nested containers, such as JSON objects returned by an API:

>>> expected_order = {
...     'id': MatchesRegex('[0-9a-z]{10}'),
...     'quantity': GreaterThan(10),
...     'shippingAddress': Contains('Dublin'),
...     'deliveryDate': ANY,
...     'amount': InRange(200, 500),
...     'items': Contains('apples') &
...              Contains('bananas') &
...              ~Contains('pears'),
... }

>>> expected_order == {
...     'id': 'cxw23fac3n',
...     'quantity': 26,
...     'shippingAddress': '18 Some Street, Dublin, London',
...     'deliveryDate': 'tomorrow',
...     'amount': 300,
...     'items': [
...         'apples',
...         'avocados',
...         'bananas',
...     ],
... }
True

>>> expected_order == {
...     'id': 'XXX',
...     'quantity': 3,
...     'shippingAddress': '18 Some Other Street, New York City, USA',
...     'deliveryDate': 'yesterday',
...     'amount': 600,
...     'items': [
...         'apples',
...         'pears',
...     ],
... }
False

This approach can be very useful in unit testing, to make tests cases shorter and easier to understand.

Installation

PyStubs has no external dependencies. To install it:

$ pip install pystubs

List of stubs

Generics:

Stub	Usage	Equivalent to	Notes
ANY	x == ANY	True
PLACEHOLDER	x == PLACEHOLDER	False	Meant to be used as a placeholder to be replaced at a later time
AnyOf	x == AnyOf([...])	x in [...]
NoneOf	x == NoneOf([...])	x not in [...]

Equality:

Stub	Usage	Equivalent to	Notes
Equal	x == Equal(y)	x == y	Useful when combined with other stubs
NotEqual	x == NotEqual(y)	x != y

Order:

Stub	Usage	Equivalent to	Notes
LessThan	x == LessThan(y)	x < y
LessThanOrEqual	x == LessThanOrEqual(y)	x <= y
GreaterThan	x == GreaterThan(y)	x > y
GreaterThanOrEqual	x == GreaterThanOrEqual(y)	x >= y
InRange	x == InRange(a, b)	a <= x < b

Containers:

Stub	Usage	Equivalent to	Notes
Contains	x == Contains(y)	y in x
HasSize	x == HasSize(y)	len(x) == y
CountOf	x == CountOf(y, c)	x.count(y) == c	Works on any iterable, even those that don't support count()
HasItems	x == HasItems({key: value})	x[key] = value

Strings:

These works on both str and bytes objects.

Stub	Usage	Equivalent to	Notes
StartsWith	x == StartsWith(y)	x.startswith(y)
EndsWith	x == EndsWith(y)	x.endswith(y)
MatchesRegex	x == MatchesRegex(p)	re.match(p, x) is not None
ContainsRegex	x == ContainsRegex(p)	re.search(p, x) is not None

Type and identity testing:

Stub	Usage	Equivalent to	Notes
Is	x == Is(y)	x is y
IsNot	x == IsNot(y)	x is not y
InstanceOf	x == InstanceOf(type)	isinstance(x, type)

Combining stubs

Stubs can be combined with the | (or), & (and), ^ (exclusive or) and ~ (not) operators. For example, the following stub expression:

>>> 'apple' == HasSize(5) & Contains('a')
True

is equivalent to the expression:

>>> len('apple') == 5 and 'a' in 'apple'
True

License

PyStubs is placed in the public domain. Feel free to do whatever you want with it and/or it's source code!