import pytest
import sys
import os

sys.path.insert(0, os.path.join(os.path.dirname(__file__), '..'))

from calculator import add, subtract, multiply, divide, is_even

def test_add():
    assert add(2, 3) == 5
    assert add(-1, 1) == 0
    assert add(0, 0) == 0

def test_subtract():
    assert subtract(5, 3) == 2
    assert subtract(0, 5) == -5
    assert subtract(-2, -3) == 1

def test_multiply():
    assert multiply(3, 4) == 12
    assert multiply(-2, 3) == -6
    assert multiply(0, 5) == 0

def test_divide():
    assert divide(10, 2) == 5
    assert divide(7, 2) == 3.5
    
    with pytest.raises(ValueError):
        divide(5, 0)

def test_is_even():
    assert is_even(4) == True
    assert is_even(3) == False
    assert is_even(0) == True