With those concepts in mind, let's see how we can actually use the unittest module in practice. For this example, we'll use test-driven development to write a simple text-analysis function. This function will take a file name as its only parameter. It will then read that file and calculate:

TDD is an iterative development process, so rather than work at the REPL we'll put the code for our tests in a file named text_analyzer.py. To start with, we'll create our first test with just enough supporting code to actually run it:

# text_analyzer.py

import unittest

class TextAnalysisTests(unittest.TestCase):
    """Tests for the ``analyze_text()`` function."""

    def test_function_runs(self):
        """Basic smoke test: does the function run."""
        analyze_text()

if __name__ == '__main__':
    unittest.main()

Ths first thing we do is import the unittest module. We then create our test case...