Testing and Debugging in Python

1. Unit Testing with unittest

The unittest module in Python provides a framework for writing and running tests. It helps ensure that your code works as expected.

Writing Your First Test Case

Here's an example of how to write a simple test case using the unittest module:

import unittest

def add(a, b):
    return a + b

class TestMathOperations(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(1, 2), 3)
        self.assertEqual(add(-1, 1), 0)
        self.assertEqual(add(0, 0), 0)

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

In this example, we define a function add and create a test case TestMathOperations that checks the functionality of the add function using assertions.

2. Debugging Techniques

Debugging is the process of identifying and resolving errors or bugs in your code. Here are some tools and techniques you can use:

• Print Statements: Inserting print() statements in your code can help track variable values and flow of execution.
• Using pdb: Python’s built-in debugger allows you to step through code, inspect variables, and evaluate expressions. You can start the debugger by adding import pdb; pdb.set_trace() in your code.
• Integrated Development Environment (IDE) Debugging: Most IDEs (like PyCharm, Visual Studio Code) offer powerful debugging tools with breakpoints, watch variables, and step execution features.

3. Example: Debugging a Function

Let’s say we have a function that is supposed to return the maximum value from a list, but it doesn't work as expected:

def find_max(numbers):
    max_value = 0
    for number in numbers:
        if number > max_value:
            max_value = number
    return max_value

print(find_max([1, 2, 3, -1, -5]))  # Expected output: 3

To debug this function, we can insert a print() statement or use pdb:

import pdb; pdb.set_trace()

By running the function with pdb, you can step through each line and inspect the max_value variable to see where it goes wrong.

4. Summary

In this tutorial, we explored unit testing using the unittest module and various debugging techniques to effectively troubleshoot Python code. Writing tests and debugging are essential skills for maintaining high-quality software.