How do you write a unit test using unittest in Python?

Writing Python unit tests with unittest: A guide

Follow these steps to write a unit test in Python using the unittest framework:

• Import the unittest module.
• Create a test case class that subclasses unittest.TestCase.
• Write test methods within the test case class to test the functions or methods you want to test.
• Use unittest assertion methods.TestCase (such as assertEqual(), assertTrue(), etc.) to check the expected outcomes.
• Optionally, use the setUp() method to set up any preconditions for the tests.
• Optionally, use the tearDown() method to clean up after each test.

The following is an example of writing a simple unit test for a Python function using unittest:

Let's suppose that we have a function called sum_numbers() that calculates the sum of two numbers.

Code:

# math_operations.py
def sum_numbers(a, b):
      return a + b

Now, let's write a unit test for the sum_numbers() function using unittest:

Code:

import unittest
from math_operations import sum_numbers
class TestSumFunction(unittest.TestCase):
    def test_positive_numbers(self):
        result = sum_numbers(10, 20)
        self.assertEqual(result, 30)
    def test_negative_numbers(self):
        result = sum_numbers(-10, -2)
        self.assertEqual(result, -12)
    def test_mixed_numbers(self):
        result = sum_numbers(8, -14)
        self.assertEqual(result, -6)
if __name__ == '__main__':
    unittest.main()

Output:

Reloaded modules: math_operations
...
----------------------------------------------------------------------
Ran 3 tests in 0.002s
OK

In the above example, we have created a test case class called TestSumFunction, which subclasses unittest.TestCase. We have written three test methods (test_positive_numbers(), test_negative_numbers(), and test_mixed_numbers()), each testing a different scenario for the sum_numbers() function.

Each test method calls the sum_numbers() function with specific arguments and uses the assertEqual() method from unittest. TestCase checks if the result matches the expected outcome.