What is the role of unit tests in the software development process?

Unit tests play a key role in the software development process:

• They check individual components (modules) of the program for correctness.
• They allow for quick detection of errors at early stages of development.
• They ensure safety when making changes — if tests pass, it means the functionality is not broken.
• They contribute to improving code design, as the tested code is usually more modular and understandable.
• They speed up debugging and maintenance.

Example in Python using unittest:

import unittest

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

class TestAddFunction(unittest.TestCase):
    def test_add_positive(self):
        self.assertEqual(add(2, 3), 5)

    def test_add_negative(self):
        self.assertEqual(add(-1, -1), -2)

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

Thus, unit tests improve the quality and reliability of software.