Is this a digit?

Write a function is_digit which receives a string as a parameter and returns a boolean. The function will return True when the parameter coincides with a character that is a digit from 0 to 9, otherwise it will return False).

You can use the following test cases to test your function:

test_case_ID  | test_input  | expected_output  | reason for testing this
--------------| ------------| -----------------|-----------------------------------
1             |    `'0'`    |  `True`          |  smallest digit
2             |  `'9'`      |  `True`          |   largest digit
3             |  `'5'`      |  `True`          |   other digit
4             |  `'12'`     |   `False`        |   it is not a digit between 0 and 9
5             |  `'-2'`     |  `False`         |  negative digit
6             |   `'hello'` |  `False`         |  string
7             |   `'r'`     |  `False`         |  a character
8             |   `'O'`     |  `False`         |  letter O, not 0

In pytest these could be implemented like:

@pytest.mark.parametrize("testcase, entrada, salida_esperada",[
    (1, '0', True),     # smallest digit
    (2, '9', True),     # largest digit
    (3, '5', True),     # other digit
    (4, '12', False),    # it is not a digit between 0 and 9 
    (5, '-2', False),    # negative digit
    (6, 'hello', False),# string
    (7, 'r', False), #character
    (8, 'O', False), #character
    ]
)

def test_is_digit(test_case_ID, test_input, expected_output): 
    assert is_digit(test_input) == expected_output, "case 0".format(test_case_ID)

Insist that the students test their programs by giving them example
pytests. And make the connection to the tables with test cases they
have seen before.