protestr 3.6.0

The state-of-the-art test fixture configurator for Python

protestr

---

Test like a pro with Protestr — the state-of-the-art test fixture configurator for Python, written in Python, tested with Protestr itself!

Table of Contents

1. TL;DR
2. Rationale
3. Getting Started
   1. Installation
   2. Defining Specs
   3. Composing Specs
   4. Ensuring Teardown
4. Documentation
5. Working Example
6. License

TL;DR

class TestFactorial(unittest.TestCase):
    @provide(n=9, expected=362880)
    @provide(n=5, expected=120)
    @provide(n=1)
    @provide(n=0, expected=1)
    def test_factorial_valid_number(self, n, expected):
        self.assertEqual(factorial(n), expected)

    @provide(n=1.5, expected="n must be an integer")
    @provide(n=between(-10000, -1), expected="n must be non-negative")
    def test_factorial_invalid_number(self, n, expected):
        try:
            factorial(n)
        except Exception as e:
            message, = e.args

        self.assertEqual(message, expected)

Also see the Working Example.

Rationale

A test fixture is any arrangement necessary for running tests, consisting of dummies, mocks, stubs, fakes, and even concrete implementations. A well-configured fixture leads to a consistent and reliable testing environment in contrast to an ill-configured one, which is a growing maintenance burden. Good fixtures can support multiple tests with modifications, such as a database seeded differently each time to test a different operation like insertion or deletion. They are also responsible for ensuring the proper disposal of resources without a miss, especially across multiple tests and files. Their configuration logic does not hijack focus from acts and assertions, and they are always reusable with all necessary adjustments. That's where Protestr comes in. It offers a declarative syntax for fixture customization to make tests concise, expressive, and reusable like never before.

Getting Started

Installation

Protestr is available as protestr on PyPI and can be installed with:

pip install protestr

Defining Specs

A fixture is technically a set of specifications (specs) "provided" to a function to resolve into actual data. The specs — usually functions — describe how different parts of the fixture form. Protestr offers a few built-in specs in protestr.specs, but you may need more. So, let's define an example geo-coordinate spec to start with. A valid geo-coordinate consists of a latitude between [-90, 90], a longitude between [-180, 180], and an altitude — something like:

from protestr import provide
from protestr.specs import between

@provide(
    lat=between(-90.0, 90.0),
    lon=between(-180.0, 180.0),
    alt=float
)
def geo_coord(lat, lon, alt):
    return lat, lon, alt

Intuitive, isn't it? Now, you can "resolve" (generate) geo-coordinates whenever you need to in the following ways:

1. Call without args:

   >>> geo_coord()
   (-28.56218898364334, 74.83481448106508, 103.16808817617861)
   

   Why invent args when Protestr can provide them?

2. Call with overridden specs:

   >>> geo_coord(
   ...     lat=choice("equator", "north pole", "south pole"),
   ...     alt=int
   ... )
   ('north pole', -107.37336459941672, 581)
   

   Here, lat and alt have been overridden by passing choice() (a built-in spec) and int. Specs can also be composed of other specs (see Composing Specs).

3. Resolve with resolve:

   >>> from protestr import resolve
   >>> resolve(geo_coord)
   (-68.79360870922969, 8.200171266070214, 691.5305890425291)
   
   >>> resolve(2*[geo_coord])
   [(41.98113033422453, 24.72261644345585, 115.79597793585394),
    (84.72658072806291, 84.71585789666494, 731.1552031682041)]
   

   resolve also works with other types, as mentioned in the Documentation.

4. Provide with provide():

   @provide(two_coords=2*[geo_coord])
   def line(two_coords):
       start, end = two_coords
       return start, end
   

   provide() can be applied to the same function multiple times to repeat it with different values. It can also be used alongside other decorators, such as patch(). More in the Documentation.

Composing Specs

A spec can be composed of other specs at any level:

>>> geo_coord(
...     lat=recipe(
...         choice(
...             choice("north pole", "90"),
...             choice("equator", "0"),
...             choice("south pole", "-90")
...         ),
...         then=str.upper
...     )
... )
('SOUTH POLE', 156.88642301107768, 984.6386910178064)

[!NOTE]

Composing specs works as long as they are passed intact.

To clarify, here's an incorrect version of the example right above:

>>> geo_coord(
...     lat=str(                            # ❌
...         choice(                         # This won't work since the
...             choice("north pole", "90"), # composed choice(...) specs
...             choice("equator", "0"),     # are consumed by str()
...             choice("south pole", "-90") # before being passed to
...         )                               # geo_coord (through lat),
...     ).upper()                           # hence they aren't intact.
... )
('<FUNCTION CHOICE.<LOCALS>.<LAMBDA> AT 0X00000261A74A2320>', -72.90254553301114, 444.88184046168556)

Ensuring Teardown

Good fixture design demands remembering to dispose of resources at the end of tests. Protestr takes care of it out of the box with the __teardown__ function. Whenever a provide()-applied function returns or terminates abnormally, it looks for __teardown__ in each (resolved) object it provided and invokes it on the object if found. So, all you need to do is define __teardown__ once in a class, and it will be called every time you provide one.

class UsersDB:
    def __init__(self, users):
        self.users = users

    def insert(self, user):
        self.users.append(user)

    def __teardown__(self):
        self.users = []

Documentation

$\large \color{gray}@protestr.\color{black}\textnormal{provide(**specs)}$

Provide resolved specs to a function.

The specs are provided automatically from keyword args in provide() to the matching parameters of the function when called with those args omitted. When specified as keyword args, they override the original specs.

@provide(
    uppercase=choice(ascii_uppercase),
    lowercase=choice(ascii_lowercase),
    digit=choice(digits),
    chars=choices(str, k=between(5, 100))
)
def password(uppercase, lowercase, digit, chars):
    return "".join((uppercase, lowercase, digit, chars))

@provide(
    password=password,
    username=choices(ascii_lowercase, k=between(4, 12))
)
def credentials(username, password):
    return username, password

>>> credentials()
('cgbqkmsehf', 'Pr8LOipCBKCBkAxbbKykppKkALxykKLOiKpiy')

>>> credentials(username="johndoe")
('johndoe', 'En2HivppppimmFaFHpEeEEEExEamp')

If provide() is applied multiple times, any call to the function repeats successively to match that number, and teardowns are performed at the end of each invocation (see Ensuring Teardown). The execution of the decorators occurs in the usual Pythonic order, i.e. bottom-up. The first (i.e. the bottom) one must provide all required specs. The subsequent ones may omit some or all specs, in which case they carry over from the previous call. The function returns the result of the last call.

@provide(
    password=password # from the previous example
    # No need to repeat username here
)
@provide(
    password=None,
    username=choices(ascii_lowercase, k=between(4, 12))
)
def credentials(username, password):
    print(f"username: {username}")
    print(f"password: {password}")
    return username, password

>>> credentials()
username: vxqoogtgr
password: None
username: sbtft
password: Ax4LzILzILZIZLpIpzIzLpzILLZIpLL
('sbtft', 'Ax4LzILzILZIZLpIpzIzLpzILLZIpLL')

provide() can also be used alongside other decorators, such as patch():

import unittest
from unittest.mock import patch

class TestPatch(unittest.TestCase):
    # this test runs twice
    @provide(intgr=between(-1, -10))
    @provide(intgr=int)
    @patch('module.ClassName2')
    @patch('module.ClassName1')
    def test_patch(self, MockClass1, MockClass2, intgr):
        module.ClassName1()
        module.ClassName2()
        self.assertIs(MockClass1, module.ClassName1)
        self.assertIs(MockClass2, module.ClassName2)
        self.assertTrue(MockClass1.called)
        self.assertTrue(MockClass2.called)
        self.assertIsInstance(intgr, int)

[!NOTE] The patches in the parameters are in the reverse order as in the list of decorators, in the usual Pythonic order. That's how patch() works. See unittest.mock - Quick Guide.

$\large \color{gray}protestr.\color{black}\textnormal{resolve(spec)}$

Resolve a spec.

The spec can be int, float, complex, float, str, a tuple, a list, a set, a dictionary, or anything callable without args.

>>> resolve(str)
'jKKbbyNgzj'

>>> resolve({"number": int})
{'number': 925}

>>> resolve({str: str})
{'RRAIvpJLKAqpLQNNVNXmExe': 'raaqSzSdfCIYxbIhuTGdxi'}

>>> from random import random
>>> resolve(random)
0.8177445321472337

>>> class Foo:
...     def __init__(self):
...         self.message = "Foo instantiated"
...
>>> resolve(Foo).message
'Foo instantiated'

$\large \color{gray}protestr.specs.\color{black}\textnormal{between(x, y)}$

Return a spec to choose a number between x and y.

x and y must be specs that evaluate to numbers. If both x and y evaluate to integers, the resulting number is also an integer.

>>> between(10, -10)()
3

>>> between(-10, 10.0)()
-4.475185425413375

>>> between(int, int)()
452

$\large \color{gray}protestr.specs.\color{black}\textnormal{choice(*elems)}$

Return a spec to choose a member from elems.

>>> colors = ["red", "green", "blue"]
>>> choice(colors)()
'green'

>>> choice(str)() # generate an str and choose a char from it
'T'

>>> choice(str, str, str)() # generate 3 strs and choose one of them
'NOBuybxrf'

$\large \color{gray}protestr.specs.\color{black}\textnormal{choices(*elems, k)}$

Returns a spec to choose k members from elems with replacement.

k must be a spec that evaluates to some natural number.

>>> choices(["red", "green", "blue"], k=5)()
['blue', 'red', 'green', 'blue', 'green']

>>> choices("red", "green", "blue", k=5)()
('red', 'blue', 'red', 'blue', 'green')

>>> choices(ascii_letters, k=10)()
'OLDpaXOGGj'

$\large \color{gray}protestr.specs.\color{black}\textnormal{sample(*elems, k)}$

Return a spec to choose k members from elems without replacement.

k must be a spec that evaluates to some natural number.

>>> colors = ["red", "green", "blue"]
>>> sample(colors, k=2)()
['blue', 'green']

>>> sample("red", "green", "blue", k=3)()
('red', 'blue', 'green')

>>> sample(ascii_letters, k=10)()
'tkExshCbTi'

>>> sample([int] * 3, k=between(2, 3))() # 2–3 out of 3 integers
[497, 246]

$\large \color{gray}protestr.specs.\color{black}\textnormal{recipe(*specs, then)}$

Return a spec to get the result of calling a given function with some given specs resolved.

then must be a function. After resolving the given specs, Protestr calls the then function with the resolved specs. If a single arg is given (i.e. one spec or a single collection of specs), it calls then with the result directly. In case of multiple args, it calls then with a tuple containing all the results.

[!TIP] then can also be a constructor.

>>> recipe(
...     sample(ascii_letters, k=5),
...     sample(digits, k=5),
...     then="".join
... )()
'yDnjU16430'

>>> recipe(int, then=str)()
'478'

>>> recipe(str, then=str.upper)()
'OXMXSJFEBWFBIL'

>>> recipe(str, then=str.encode)()
b'IHbNrZeSYYLm'

>>> recipe(5, then=lambda i: i**2)()
25

Working Example

The complete working example available in tests/examples/ should be self-explanatory. If not, please refer to Getting Started and Documentation to become familiar with a few concepts. Here's an excerpt:

# tests/examples/test_examples.py

import tests.examples.specs as specs
...
...

class TestExamples(unittest.TestCase):
    ...
    ...

    @provide(
        password=recipe(
            choices(digits, k=5),
            choices(ascii_uppercase, k=5),
            then="".join
        ),
        expected="Password must contain a lowercase letter"
    )
    @provide(
        password=recipe(
            choices(digits, k=5),
            choices(ascii_lowercase, k=5),
            then="".join
        ),
        expected="Password must contain an uppercase letter"
    )
    @provide(
        password=choices(ascii_letters, k=8),
        expected="Password must contain a number"
    )
    @provide(
        password=choices(str, k=7),
        expected="Password must be at least 8 chars",
        db=specs.testdb,
        user=specs.user
    )
    @patch("tests.examples.fakes.os.getenv")
    def test_insert_user_with_invalid_password(
        self, getenv, db, user, password, expected
    ):
        getenv.side_effect = [8]

        user.password = password

        try:
            db.insert(user)
        except Exception as e:
            message, = e.args

        self.assertEqual(message, expected)

        getenv.assert_called_once_with("MIN_PASSWORD_LEN")

    ...
    ...

if __name__ == "__main__":
    unittest.main()

If you're curious, here are the specs we defined for the example:

# tests/examples/specs.py

from tests.examples.fakes import User, UsersDB
...
...

@provide(
    digit=choice(digits),                 # password to contain a
    uppercase=choice(ascii_uppercase),    # number, an uppercase and a
    lowercase=choice(ascii_lowercase),    # lowercase letter, and be
    chars=choices(str, k=between(5, 100)) # 8–15 characters long
)
def password(uppercase, lowercase, digit, chars):
    return "".join((uppercase, lowercase, digit, chars))


@provide(
    id=str,
    firstname=choice("John", "Jane", "Orange"),
    lastname=choice("Smith", "Doe", "Carrot"),
    username=choices(ascii_lowercase, k=between(5, 10)),
    password=password
)
def user(id, firstname, lastname, username, password):
    return User(id, firstname, lastname, username, password)


@provide(users=3*[user])
def testdb(users):
    return UsersDB(users)

License

protestr is distributed under the terms of the MIT license.