validparentheses.py

from unittest import TestCase, main

def valid_parentheses(string):
    x = 0
    for char in string:
        if char == '(':
            x += 1
        elif char == ')':
            if x == 0:
                return False
            x -= 1
    return x == 0

class TestValidParenthesis(TestCase):

    def test_open_only_is_invalid(self):
        self.assertNotValid("(")

    def test_close_only_is_invalid(self):
        self.assertNotValid(")")

    def test_valid_section_first_then_open_is_invalid(self):
        self.assertNotValid("((()))(")

    def test_valid_section_first_then_close_is_invalid(self):
        self.assertNotValid("((())))")

    def test_one_matching_paren_is_valid(self):
        self.assertIsValid("()")

    def test_three_matching_paren_is_invalid(self):
        self.assertIsValid("((()))")

    def test_many_paren_sections_is_valid(self):
        self.assertIsValid("((()))()((((()))))(())")

    def assertNotValid(self, parens):
        self.assertFalse(valid_parentheses(parens))

    def assertIsValid(self, parens):
        self.assertTrue(valid_parentheses(parens))

if __name__ == "__main__":
    main()