Variable Size Box

Write a function variable_size_box that similarly to the function from the previous assignment nested_box(), returns a string with a box. In this case, also using a nested for loop, the function should accept two optional parameters with the size and the character to use. Example:

variable_size_box()
"""
****
****
****
****
"""

variable_size_box(3, '@')
"""
@@@
@@@
@@@
"""

variable_size_box(5, '.')
"""
.....
.....
.....
.....
.....
"""
import unittest

DEFAULT_EXPECTED_BOX = """
****
****
****
****
""".lstrip()

BIGGER_BOX_WITH_SPECIAL_CHARACTER = """
;;;;;
;;;;;
;;;;;
;;;;;
;;;;;
""".lstrip()

class BoxTestCase(unittest.TestCase):

    def test_nested_box(self):
        self.assertEqual(
            variable_size_box(), DEFAULT_EXPECTED_BOX)

    def test_bigger_box_with_special_char(self):
        self.assertEqual(
            variable_size_box(5, ';'), BIGGER_BOX_WITH_SPECIAL_CHARACTER)