Nested Box

Write a simple function nested_box that, using nested for loops, returns a string with a box like the one shown below:

****
****
****
****
import unittest

EXPECTED_BOX = """
****
****
****
****
""".lstrip()


class BoxTestCase(unittest.TestCase):

    def test_nested_box(self):
        self.assertEqual(nested_box(), EXPECTED_BOX)