d = {'a': 123, 'b': 456}
assert ('a', 123) in d.items()
assert ('b', 456) in d.items()
assert ('a', 123, 3) not in d.items()
assert () not in d.items()

>>> a={'a':1}
>>> 1 in a.items()
False
>>> 'a' in a.items()
False
>>>('a') in a.items()
False

>>>>> a={'a':1}
>>>>> 1 in a.items()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Expected type 'tuple', not 'int'

>>>>> 'a' in a.items()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Expected type 'tuple', not 'str'

>>>>> ('a') in a.items()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Expected type 'tuple', not 'str'