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<h1>Unit testing</h1>

<p>Unit testing is a method of determining the correctness of a single function

isolated from a larger codebase. The idea is that if all the atomic units

of an application work as intended in isolation, then integrating them

together as intended is much easier.</p>

<h2>Why is unit testing important?</h2>

<p>Unit testing is just one form of <a href="/testing.html">testing</a> that works in

combination with other testing approaches to wring out the bugs from a

piece of software being developed. When several functions and classes are

put together it's often difficult to determine the source of a problem if

several bugs are occurring at the same time. Unit testing helps eliminate

as many of the individual bugs as possible so when the application comes

together as a whole the separate parts work as correct as possible. Then

when issues arise they can often be tracked down as unintended consequences

of the disparate pieces not fitting together properly.</p>

<h2>Unit testing tools</h2>

<p>There are many tools for creating tests in Python. Some of these tools, such

as pytest, replace the built-in unittest framework. Other tools, such as

nose, are extensions that ease test case creation. Note that many of these

tools are also used for <a href="/integration-testing.html">integration testing</a>

by writing the test cases to exercise multiple parts of code at once.</p>

<p><a href="https://docs.python.org/3/library/unittest.html">unittest</a>

is the built-in standard library tool for testing Python code.</p>

<p><a href="http://pytest.org/latest/">pytest</a> is a complete testing tool that

emphasizes backwards-compatibility and minimizing boilerplate code.</p>

<p><a href="https://nose.readthedocs.org/en/latest/">nose</a> is an extension to

unittest that makes it easier to create and execute test cases.</p>

<p><a href="https://github.com/Yelp/Testify/">testify</a> was a testing framework

meant to replace the common unittest+nose combination. However, the team

behind testify is transitioning to pytest so it's recommended you do

not use testify for new projects.</p>

<h3>Unit testing resources</h3>

<p><a href="http://www.diveintopython3.net/unit-testing.html">Dive into Python 3's chapter on unit testing</a>

has a complete example with code and a detailed explanation for creating

unit testing with the

<a href="https://docs.python.org/3/library/unittest.html">unittest</a> module.</p>

<p><a href="https://www.twilio.com/blog/2014/03/unit-testing-your-twilio-app-using-pythons-flask-and-nose.html">Unit Testing Your Twilio App Using Python’s Flask and Nose</a>

is a detailed tutorial for using the nose test runner for ensuring a

Flask application is working properly.</p>

<p><a href="https://jeffknupp.com/blog/2013/12/09/improve-your-python-understanding-unit-testing/">Understanding unit testing</a>

explains why testing is important and shows how to do it effectively in

your applications.</p>

<p><a href="http://www.drdobbs.com/testing/unit-testing-with-python/240165163">Unit testing with Python</a>

provides a high-level overview of testing and has diagrams to demonstrate

what's going on in the testing cycle.</p>

<p>The Python wiki has a page with a list of

<a href="https://wiki.python.org/moin/PythonTestingToolsTaxonomy">Python testing tools and extensions</a>.</p>

<p><a href="http://blog.fogcreek.com/working-effectively-with-unit-tests-interview-with-jay-fields/">Working Effectively with Unit Tests</a>

is an interview with the author of a book by the title where he shares

some of the insight he's learned on the topic.</p>

<p><a href="http://blog.kevinastone.com/generate-your-tests.html">Generate your tests</a>

shows how to write a test generator that works with the <code>unittest</code>

framework.</p>

<p><a href="http://ivory.idyll.org/articles/nose-intro.html">An Extended Introduction to the nose Unit Testing Framework</a>

shows how this test runner can be used to write basic test suites.

While the article is from 2006, it remains relevant today for learning

how to use nose with your projects.</p>

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