String Rotation: Assumeyou have a method isSubstringwhich checks ifoneword isa substring of another. Given two strings, sl and s2, write code to check if s2 is a rotation of sl using only one call to isSubstring (e.g., "waterbottle" is a rotation of"erbottlewat").

rotation.py

class Rotation:

    @staticmethod
    def is_substring(s1, s2):
        """Checks if s2 is a substring of s1

        Args:
            s1 (string) string input
            s2 (string) rotation of s1

        Returns:
            True if s2 is a substring of s1
            False otherwise
        """
        # we should check somewhere here if s1 is indeed a rotation of s2
        if len(s1) != len(s2):
            return False

        s = s2 + s2
        return s1 in s

import unittest
class TestRotation(unittest.TestCase):

    def test_example(self):
        self.assertTrue(Rotation.is_substring("waterbottle", "erbottlewat"))

    def test_empty(self):
        self.assertTrue(Rotation.is_substring("",""))

    def test_not_rotation_diff_length(self):
        self.assertFalse(Rotation.is_substring("a", "ba"))

    def test_not_rotation_same_length(self):
        self.assertFalse(Rotation.is_substring("aa", "ba"))

    def test_rotation_same_string(self):
        self.assertTrue(Rotation.is_substring("aa", "aa"))

    def test_rotation_stuff(self):
        self.assertTrue(Rotation.is_substring("andrew", "rewand"))

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