python string split method, with only integer argument, no delimiter is used

import unittest

class TestStringMethods(unittest.TestCase):

    def test_split(self):
        s = 'hello world'
        self.assertEqual(s.split(), ['hello', 'world'])
        # check that s.split fails when the separator is not a string
        with self.assertRaises(TypeError):
            s.split(2)

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

what is the use of s.split(2) method? what author wants to accomplish from this code. what split method of string module do when it is call using only integer argument?