test_correct :-
TestCases = [123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345],
foreach( ( member(TestCase, TestCases),
middle_3_digits(TestCase, Result) ),
format('Middle 3 digits of ~w ~30|: ~w~n', [TestCase, Result])
).