Quickstart

So, you got Attest installed? Great! Let’s get started writing tests!

The PyPI Metadata Module

The Python Package Index exposes metadata for projects as JSON. Let’s write a simple module to read this data and test it with Attest!

The first order of business is to design the API we want. A good way to do this is to draft the documentation first - this is dubbed Readme Driven Development and goes well in hand with test driven development.

Suppose we came up with an API like this:

>>> package = Package('Attest')
>>> package.author
u'Dag Odenhall'
>>> package.summary
u'Modern, Pythonic unit testing.'

Now we want to write the tests. It’s a good idea to do this before we write any actual code for the module itself because the tests lets us verify that the eventual code does what we want and we can avoid manual testing.

Here’s the API defined as tests:

from attest import Tests
from pypilib import Package  # our fictional module

pypi = Tests()

@pypi.test
def properties():
    package = Package('Attest')
    assert package.author == 'Dag Odenhall'
    assert package.summary == 'Modern, Pythonic unit testing.'

if __name__ == '__main__':
    pypi.run()

Save it as tests.py and run it. What happens?

$ python tests.py
Traceback (most recent call last):
  File "tests.py", line 2, in <module>
    from pypilib import Package  # our fictional module
ImportError: No module named pypilib

As expected we get an ImportError because we haven’t created our module yet. So that’s the next step! First we just stub the class:

class Package(object):
    pass

This should fail because this constructor doesn’t take any arguments. Let’s confirm this:

$ python tests.py
[100%] 1 of 1 Time: 0:00:00

properties
─────────────────────────────────────────────────────────────────────
Traceback (most recent call last):
  File "tests.py", line 8, in properties
    package = Package('Attest')
TypeError: object.__new__() takes no parameters

Failures: 1/1 (0 assertions)

Just as expected. OK - so we write a custom constructor:

class Package(object):
    def __init__(self, name):
        pass

Still fails:

Traceback (most recent call last):
  File "tests.py", line 9, in properties
    assert package.author == 'Dag Odenhall'
AttributeError: 'Package' object has no attribute 'author'

It’s time to write some real code! Here’s our working module:

import json
import urllib2

class Package(object):

    def __init__(self, name):
        url = 'http://pypi.python.org/pypi/%s/json' % name
        data = json.loads(urllib2.urlopen(url).read())
        self.author = data['info']['author']
        self.summary = data['info']['summary']

Now the tests pass:

$ python tests.py
[100%] 1 of 1 Time: 0:00:00

Failures: 0/1 (0 assertions)