Clean Tests

T1: Insufficient Tests

Test everything that could possibly break. Use coverage tools as a guide, not a goal.

# Bad - only tests happy path
def test_divide():
    assert divide(10, 2) == 5

# Good - tests edge cases too
def test_divide_normal():
    assert divide(10, 2) == 5

def test_divide_by_zero():
    with pytest.raises(ZeroDivisionError):
        divide(10, 0)