TDD in Python and PyCharm

PyCharm encourages TDD

Example of a unit test:

    def test_parse_input(self):
        self.assertDictEqual(self.expected_parse, self.data_packer.parse_input())
        self.assertEqual(self.expected_parse["T"], self.data_packer.T)
        self.assertListEqual(self.expected_parse["challenges"], self.data_packer.challenges)

Google Code Jam's Data Packing problem

Input:

Number of challenges, followed by file and disc size info.

3
3 100
10 20 70
4 100
30 40 60 70
5 100
10 20 30 40 60

Output:

The number of discs needed to store the files.

Case #1: 2
Case #2: 2
Case #3: 3

First Try: Just write the code. Test at the end.

Solution 1

Summary

• Time: 75 minutes (40 minutes spent debugging monster function)
• Cyclomatic complexity: worst method had 9 and a B grade
• Coding style: ugly. Will be hard to understand next week.

Second Try: Follow strict TDD

TDD Unit Tests for Solution 2

Solution 2 code

• Time: 45 minutes (almost no time spent debugging)
• Cyclomatic complexity: worst method had 6 and got straight A's for all methods
• Coding style: very good. Compartmentalized design will make it easy to understand and refactor. Unit tests will catch any future issues that could arise from new requirements.

Some useful unittest constructs:

• setUp(): Let's you keep access any data that you want to keep around for all (or most of) the tests.
• tearDown(): The opposite of setUp()
• fail(): Force a test to fail. Useful in TDD when you're still in the process of writing your tests.
• various asserts:
  • assertEquals()
  • assertIsNone()
  • assertListEquals()
  • assertDictEquals()
  • assertRaises()
  • many more

Some more advanced techniques:

• Mocking and patching
• BDD