def test_same_letters(self):
self.assertEqual(count_letters("a"), {"a": 1})
self.assertEqual(count_letters("aa"), {"a": 2})
def test_distinct_letters(self):
self.assertEqual(count_letters("ab"), {"a": 1, "b"})
def test_if_exists(self):
self.assertEqual(count_letters(""), {})
def test_different_letters(self):
self.assertEqual(count_letters("b"), {"b": 1})