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

class TestCalculator(unittest.TestCase):

    def test_add(self):
        self.assertEqual(add(2, 3), 5)
        self.assertEqual(add(-1, 1), 0)
        self.assertEqual(add(-1, -1), -2)

    def test_subtract(self):
        self.assertEqual(subtract(3, 2), 1)
        self.assertEqual(subtract(-1, 1), -2)
        self.assertEqual(subtract(-1, -1), 0)

    def test_multiply(self):
        self.assertEqual(multiply(2, 3), 6)
        self.assertEqual(multiply(-1, 1), -1)
        self.assertEqual(multiply(-1, -1), 1)

    def test_divide(self):
        self.assertEqual(divide(6, 3), 2)
        self.assertEqual(divide(-1, 1), -1)
        self.assertEqual(divide(-1, -1), 1)
        with self.assertRaises(ValueError):
            divide(1, 0)

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