Tag Archives: testing

I am very bad at writing tests

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… but I _think_ I might be getting a little better.

At least these days when I am writing some script (almost certainly in [Python][python]) I start out by intending to write tests. I usually fail because I haven’t learnt to think in terms of writing code that can be easily tested.

[Mark Pilgrim][pilgrim]’s [Dive Into Python][dive] has great stuff on how to approach a problem by [defining the tests first and gradually filling in the code][divetest] that satisfies the test suite. One day I may be able to work like that, until then I work by writing a concise docstring, then stubbing out the function. Once the function is in a state where it might actually return a meaningful result I can play with it in the Python interpreter and start adding useful [doctests][doctest] to the [docstring][docstring].

What really helps is to break the logic out into tiny pieces where ideally each piece returns the result of transforming the input (which I think is known as a [functional approach][functional]). By doing this I can have tests for most of the code and those functions that have a lot of conditional logic, those functions that are harder to write tests for, will at least be relying on sub-routines that are themselves well tested.

I can dream.

[python]: http://www.python.org/
[pilgrim]: http://diveintomark.org/
[dive]: http://www.diveintopython.org/
[divetest]: http://diveintopython.org/unit_testing/stage_1.html
[doctest]: http://docs.python.org/library/doctest.html
[functional]: http://en.wikipedia.org/wiki/Functional_programming
[docstring]: http://www.python.org/dev/peps/pep-0257/

Django test database runner as a context manager

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In my last post I mentioned it might be an idea to [wrap up the Django test
database setup / teardown in a context manager][lastpost] for use with [Python’s
`with` statement][pythonwith]. Here’s my first stab, which seems to work.

from contextlib import contextmanager

@contextmanager
def test_db_connection():
“””A context manager for Django’s test runner.

For Python 2.5 you will need
from __future__ import with_statement
“””

from django.conf import settings
from django.test.utils import setup_test_environment, teardown_test_environment
from django.db import connection

setup_test_environment()

settings.DEBUG = False
verbosity = 0
interactive = False

old_name = settings.DATABASE_NAME
connection.creation.create_test_db(verbosity, autoclobber=not interactive)

yield connection

connection.creation.destroy_test_db(old_name, verbosity)
teardown_test_environment()

All of this requires Python 2.5 or later.

So with that snippet you could write a test something like so:

import unittest

class MyTestCase(unittest.TestCase):
def test_myModelTest(self):
with test_db_connection():
from myproject.myapp.models import MyModel

obj = MyModel()
obj.save()
self.assert_(obj.pk)

… and just as with Django’s `manage.py test` command the objects would be
created within the test database then destroyed when the
`with test_db_connection()` block is finished.

Everything’s going to be hunky dory.

[lastpost]: http://reliablybroken.com/b/2009/03/creating-a-django-test-database-for-unit-testing/
[pythonwith]: http://docs.python.org/reference/datamodel.html#context-managers

Creating a Django test database for unit testing

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I needed to run tests involving a Django application but without using the
`manage.py test` management command. So I need my own test suite that
sets up the test database and drops it after, leaving my real database untouched.

As of Django 1.0.2 the default behaviour for the test runner is the [`run_tests`
function in `django.test.simple`][runtests]. Here is the bones of that function
with the required setup and teardown calls.

from django.conf import settings
from django.test.utils import setup_test_environment, teardown_test_environment

verbosity = 1
interactive = True

setup_test_environment()
settings.DEBUG = False
old_name = settings.DATABASE_NAME

from django.db import connection
connection.creation.create_test_db(verbosity, autoclobber=not interactive)

# Here you run tests using the test database and with mock SMTP objects

connection.creation.destroy_test_db(old_name, verbosity)
teardown_test_environment()

Hmmm… Wouldn’t this be a good candidate to be wrapped up for use with
[Python 2.5’s `with` statement][with]?

[runtests]: http://code.djangoproject.com/browser/django/tags/releases/1.0.2/django/test/simple.py#L102
[with]: http://docs.python.org/reference/datamodel.html#context-managers