def test_simple_letters(self):
     self.assertEqual(count_letter("a"), {"a":1})
     self.assertEqual(count_letter("aa"), {"a":2})
 def test_distinct_letters(self):
     self.assertEqual(count_letter("ab"), {"a":1, "b":1})
 def test_if_exists(self):
     self.assertEqual(count_letter(""), {})
 def test_differernt_letters(self):
     self.assertEqual(count_letter("b"), {"b":1})