"""
    Ejemplo de implementacion de test y pruebas de la funcion factorial

        factorial(0) = 1
        factorial(1) = 1
        factorial(2) = 2
        factorial(3) = 6
        factorial(4) = 24
        factorial(5) = 120

        n! = n*(n-1)*(n-2)*...*1
"""
import unittest

class ErrorValorNegativo(Exception):
    pass

# Esta función se puede definir de forma recursiva o iterativa
# Para este caso se define usando recursión.
def factorial(n):
    if n < 0:
        raise ErrorValorNegativo("Número Negativo")
    elif n == 0:
        return 1
    elif n == 1:
        return 1
    else:
        return n * factorial(n - 1)

class FactoriaTestCase(unittest.TestCase):

    def test_factorial_numero_negativo(self):
        self.assertRaises(ErrorValorNegativo, factorial, -1)

    def test_factorial_0(self):
        self.assertEqual(1, factorial(0))

    def test_factorial_1(self):
        self.assertEqual(1, factorial(1))

    def test_factorial_2(self):
        self.assertEqual(2, factorial(2))

    def test_factorial_3(self):
        self.assertEqual(6, factorial(3))

    def test_factorial_4(self):
        self.assertEqual(24, factorial(4))

    def test_factorial_5(self):
        self.assertEqual(120, factorial(5))

    def test_factorial_6(self):
        self.assertEqual(720, factorial(6))

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

#for i in range(10):
#    print(factorial(i))