stack.py

import unittest

class Stack:
    stack = []
    size = 0

    def push(self, i):
        self.stack.append(i)
        self.size += 1
        pass

    def pop(self):
        if self.size == 0:
            return None
        self.size -= 1
        return self.stack[self.size]
        pass

    def peek(self):
        pass

class TestStack(unittest.TestCase):

    def setUp(self):
        pass

    def test_stackInitializesWithZeroSize(self):
        stack = Stack()
        self.assertEqual(stack.size, 0)

    def test_pushAddsToStackSize(self):
        stack = Stack()
        stack.push(2)
        self.assertEqual(stack.size, 1)

    def test_popEmptyStackReturnsNone(self):
        stack = Stack()
        item = stack.pop()
        self.assertEqual(item, None)

    def test_popStackWithOneItemReturnsItem(self):
        stack = Stack()
        stack.push(2)
        item = stack.pop()
        self.assertEqual(item, 2)
        self.assertEqual(stack.size, 0)

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