Is it possible to describe a development approach where tests are written before the implementation of code, and explain its main principles?

The development approach where tests are written before the code implementation is called Test-Driven Development (TDD) — development through testing.

Main principles of TDD:

1. Write a test — first, an automated test is created that describes the required behavior or functionality.

2. Run the test and ensure it fails — since the functionality is not yet implemented, the test should fail.

3. Write minimal code to pass the test — implement only what is necessary to pass the test.

4. Refactoring — improve the code while keeping the tests passing.

5. Repeat the cycle — add new tests and functionality.

TDD helps create more reliable and maintainable code, reduces bugs, and improves design.

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()

First, write the tests, then implement the add function.