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Python Assertion Helpers inspired by Shouldly

Project Description


Python Assertion Helpers Inspired by Shouldly


- forbiddenfruit
- a version of python with which forbidden fruit will work
(must implement the CTypes/CPython Python API)
- Python 2.7 or 3.3
(it may work with other versions, such as other 3.x versions,
but it has not been tested with these versions)





>>> import should_be.all
>>> class Cheese(object):
... crackers = 3
>>> swiss = Cheese()
>>> swiss.crackers.should_be(4)
AssertionError: swiss.crackers should have been 4, but was 3

.. note::

Because of the way the Python REPL shows stack traces, if the 'should_be'
assertion is typed in a line on the REPL, '(unknown)' will show instead
of 'swiss.crackers'. This is not an issue when the 'should_be' statement
is in a file instead.


The easy way

.. code-block:: bash

$ sudo pip install

The slightly-less-easy way

.. code-block:: bash

$ git clone
$ cd should_be
$ ./ build
$ sudo ./ install


.. role:: python(code)
:language: python

Writing your own assertions is fairly easy. There are two core parts of
ShouldBe: :python:`BaseMixin` and `should_follow`.

All assertions should be placed in classes that inherit from :python:`BaseMixin`.
:python:`BaseMixin` provides the basic utilities for extending built-in objects
with your assertions.

The class which holds your assertions should have a class variable called
:python:`target_class`. This is the class on which your assertions will be run.
By default, this is set to :python:`object`. If you wish to have your assertions
run on :python:`object`, there are a few additional considerations to make (see
warning below).

Then, assertions should be defined as instance methods. Each method should call
:python:`self.should_follow` one or more times. Think of `should_follow` as `assertTrue`
on steroids. It has the following signature:
:python:`should_follow(self, assertion, msg=None, **kwargs)`. Obviously, assertion is
an expression which, when :python:`False`, causes `should_follow` to raise an `AssertionError`.
So far, pretty normal. :python:`msg` is where things get interesting. `msg` should be
a new-style Python format string which contains only named substitutions. By
default, :python:`should_follow` will pass the `txt` and `self` keys to the `format` method,
in addition to any keyword arguments passed to :python:`should_follow`. `self` is, obviously,
the current object. :python:`txt` is the code that represents the current object. For instance,
if we wrote :python:`(3).should_be(4)`, `txt` would be '(3)'. If we wrote
:python:`cheese.variety.should_be('cheddar')`, `txt` would be 'cheese.variety'.

Once all of your assertions are written, you can simply write
:python:`MyAssertionMixin.mix()` to load your assertions. A `setuptools`
hook is on the way for autoloading custom assertion mixins
with :python:`import should_be.all`.

.. warning::

When you extend object, you need to also create the proper mixins for
:python:`NoneType`, since `None` doesn't have instance methods per-se (since
:python:`self` gets set to `None`, the Python interpreter complains). Thankfully,
this is fairly easy. Simply create a class which inherits from :python:`NoneTypeMixin`,
and set the class variable :python:`source_class` to the name of your `object` assertions
class. You can then simply run :python:`MyNoneTypeMixin.mix()`, and your methods will
be automatically retrieved and converted from your :python:`object` mixin class.

.. note::

Assertions for ABCs (such as Sequence) will be automatically mixed in to 'registered'
classes that do not inherit methods from the ABCs normally (such as list, etc) when
the :python:`mix()` method is called (this will also check for classes that are registered
to subclasses of the ABCs).

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