/expecter

Expecter Gadget: better expectations (assertions) for Python.

Primary LanguagePython

BASICS

Expecter Gadget helps you to write assertions. Never again will you forget which is expected and which is actual!

Basic expectations are easy:

>>> from expecter import expect
>>> expect('some' + 'thing') == 'something'
expect('something')
>>> expect(1) > 100
Traceback (most recent call last):
...
AssertionError: Expected something greater than 100 but got 1

Just read the expectations like a sentence. "expect(2) == 1 + 1" reads as "Expect 2 to equal 1 + 1". Obviously, the expectation is about 2, and it's being compared to 1 + 1. No ambiguity!

EXCEPTIONS

Expectations about exceptions use the "with" statement. Everything is good if the expected exception is raised:

>>> from __future__ import with_statement
>>> with expect.raises(KeyError):
...     {}[123]

If it's not raised, Expecter Gadget will raise an AssertionError:

>>> with expect.raises(KeyError):
...     pass
Traceback (most recent call last):
...
AssertionError: Expected an exception of type KeyError but got none

Exceptions that don't match the expected one will not be swallowed, so your test will error as you expect:

>>> from __future__ import with_statement
>>> with expect.raises(NameError):
...     {}[123]
Traceback (most recent call last):
...
KeyError: 123

CUSTOM EXPECTATIONS

You can add a custom expectation with the add_expectation method. You give it a predicate that should return true if the expectation succeeds and false if it fails. All expectation objects will grow a method with the name of your predicate method (so don't use a lambda). Appropriate exception messages will be generated when your predicate fails:

>>> import expecter
>>> def can_meow(thing):
...     return thing == 'kitty'
>>> expecter.add_expectation(can_meow)
>>> expect('kitty').can_meow()
>>> expect('puppy').can_meow()
Traceback (most recent call last):
...
AssertionError: Expected that 'puppy' can_meow, but it can't

API DOCUMENTATION

See http://expecter-gadget.readthedocs.org/en/latest/