import unittest


def kth_to_last_node(k, head):
    # Return the kth to last node in the linked list
    current = head
    if not head or k<=0:
        raise Exception('No head/ k <=0')
    for i in range(k-1):
        current = current.next
        if not current:
            raise Exception('Less than ', k, 'nodes')
    ending_node= current
    kth_to_last = head

    while ending_node.next:
        ending_node = ending_node.next
        kth_to_last = kth_to_last.next
    return kth_to_last



# Tests

class Test(unittest.TestCase):

    class LinkedListNode(object):

        def __init__(self, value, next=None):
            self.value = value
            self.next  = next

        def get_values(self):
            node = self
            values = []
            while node is not None:
                values.append(node.value)
                node = node.next
            return values

    def setUp(self):
        self.fourth = Test.LinkedListNode(4)
        self.third = Test.LinkedListNode(3, self.fourth)
        self.second = Test.LinkedListNode(2, self.third)
        self.first = Test.LinkedListNode(1, self.second)

    def test_first_to_last_node(self):
        actual = kth_to_last_node(1, self.first)
        expected = self.fourth
        self.assertEqual(actual, expected)

    def test_second_to_last_node(self):
        actual, count = kth_to_last_node(2, self.first)
        expected = self.third
        self.assertEqual(actual, expected)

    def test_first_node(self):
        actual, count = kth_to_last_node(4, self.first)
        expected = self.first
        self.assertEqual(actual, expected)

    def test_k_greater_than_linked_length(self):
        with self.assertRaises(Exception):
            kth_to_last_node(5, self.first)

    def test_k_is_zero(self):
        with self.assertRaises(Exception):
            kth_to_last_node(0, self.first)


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


# Tests

class Test(unittest.TestCase):
    class LinkedListNode(object):

        def __init__(self, value, next=None):
            self.value = value
            self.next = next

        def get_values(self):
            node = self
            values = []
            while node is not None:
                values.append(node.value)
                node = node.next
            return values

    def setUp(self):
        self.fourth = Test.LinkedListNode(4)
        self.third = Test.LinkedListNode(3, self.fourth)
        self.second = Test.LinkedListNode(2, self.third)
        self.first = Test.LinkedListNode(1, self.second)

    def test_first_to_last_node(self):
        actual = kth_to_last_node(1, self.first)
        expected = self.fourth
        self.assertEqual(actual, expected)

    def test_second_to_last_node(self):
        actual = kth_to_last_node(2, self.first)
        expected = self.third
        self.assertEqual(actual, expected)

    def test_first_node(self):
        actual = kth_to_last_node(4, self.first)
        expected = self.first
        self.assertEqual(actual, expected)

    def test_k_greater_than_linked_length(self):
        with self.assertRaises(Exception):
            kth_to_last_node(5, self.first)

    def test_k_is_zero(self):
        with self.assertRaises(Exception):
            kth_to_last_node(0, self.first)


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