Testing with pytest

# pip install pytest
# Run: pytest test_file.py -v

# pytest uses simple assert statements!
def add(a, b):
    return a + b

def multiply(a, b):
    return a * b

# Test functions (start with test_)
def test_add():
    assert add(2, 3) == 5
    assert add(-1, 1) == 0
    assert add(0, 0) == 0

def test_multiply():
    assert multiply(3, 4) == 12
    assert multiply(-2, 3) == -6

# Test exceptions
def test_divide_by_zero():
    try:
        result = 10 / 0
        assert False, "Should have raised"
    except ZeroDivisionError:
        pass  # Expected!

# Parametrized tests
import functools

test_cases = [
    (2, 3, 5),
    (0, 0, 0),
    (-1, 1, 0),
    (100, 200, 300),
]

def test_add_parametrized():
    for a, b, expected in test_cases:
        assert add(a, b) == expected, f"add({a}, {b}) should be {expected}"

# Fixtures (setup/teardown)
# @pytest.fixture
# def sample_data():
#     return [1, 2, 3, 4, 5]
# 
# def test_sum(sample_data):
#     assert sum(sample_data) == 15

# Run all tests
print("=== pytest Demo ===")
tests = [test_add, test_multiply, test_divide_by_zero, test_add_parametrized]
for test in tests:
    try:
        test()
        print(f"  ✅ {test.__name__} PASSED")
    except AssertionError as e:
        print(f"  ❌ {test.__name__} FAILED: {e}")

print(f"\n{len(tests)} tests passed!")

# pytest commands:
print("\n=== pytest Commands ===")
print("pytest                  # run all tests")
print("pytest -v               # verbose output")
print("pytest -k 'test_add'    # run matching tests")
print("pytest --cov=mymodule   # code coverage")