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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="https://realpython.com/blog/python/the-minimum-viable-test-suite/">The Minimum Viable Test Suite</a>

shows how to set unit tests and integration tests for a Flask example

application.</p>

<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://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>

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<div class="panel-heading"><h3 class="panel-head">Unit Testing</h3></div>

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