Only integers

Define a function add_only_integers that receives two numbers and returns
the sum of them ONLY if they’re both integers. If that’s not the case, the
function should return the string "invalid parameters".


>>> add_only_integers(2, 3)
>>> add_only_integers(2, 'what')
'invalid parameters'
import unittest

class AddOnlyIntegersTestCase(unittest.TestCase):

    def test_integers(self):
        self.assertEqual(add_only_integers(2, 3), 5)

    def test_not_integers(self):
        self.assertEqual(add_only_integers(2, 'what'), 'invalid parameters')