As a demonstration of unit testing in Python , we will consider a class implementing stop list functionality. A stop list is a tool used in building search engines and other retrieval systems. In such systems, documents are usually indexed by the words they contain. A document on the organization of the U.S. government would probably contain the terms "President", "Senate", and "Supreme Court" among others. The document would be indexed by these words so that users who type some combination of them into a search form would see this document appear in their list of search results.
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To develop our stop list class we will use a test-driven development (TDD) application of unit testing. In TDD, before we implement a feature (e.g., a method within our stop list class), we first write a test case that, once the new feature is implemented, will ensure it meets specification. The motivating idea for TDD is that the developer should first reflect on a feature's specification and how it will be used in systems of which it is a part.
In Python, as is the case with most languages, unit testing is automated within a framework that takes as input, a test case and code on which to run the test case. As output, it generates a test report on the results of having executed the test case. The unit testing framework in the Python library is implemented in the unittest module. This tutorial will describe one approach to using unittest. For a broader perspective, see the official documentation on unittest for more information.
A test case is a class containing methods for testing each requirement of a feature to ensure all aspects of the specification are implemented and function correctly. We implement test cases as subclasses of unittest.TestCase. Our first step will be to implement an empty test case and run it to be sure we have the basics in place. Following is a code listing for our initial test case in a file called term_test.py.
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| title | term_test.py |
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