#!/usr/bin/python


def finding_gcd(a, b):
    ''' implements the greatest common divider algorithm '''
    while(b != 0):
        result = b
        a, b = b, a % b        
    return result


def test_finding_gcd():
    number1 = 21
    number2 = 12
    assert(finding_gcd(number1, number2) == 3)
    print('Tests passed!')

if __name__ == '__main__':
    test_finding_gcd()