Python code to check if an array has a sequence (1,3,4)
By PEP 8, doesSeqAppear should be does_seq_appear. You used the right naming convention for your unit tests, though. Personally, I would prefer def contains_seq(arr, seq=[1, 3, 4]).

Your arr_len &lt; 3 test is superfluous and should therefore be eliminated. Don't write a special case when the regular case works correctly and just as quickly.

Your all(isinstance(item, int) for item in int_arr) check was not specified in the problem, and is therefore harmful. The question does not say that doesSeqAppear([3.1, 1, 3, 4]) should return False, nor does it say that it should fail with an exception. In fact, by my interpretation, it does contain the magic sequence and should therefore return True. In any case, you have wasted a complete iteration of the list just to perform a check that wasn't asked for.

Checking isinstance(int_arr, list) is un-Pythonic, since duck-typing is the norm in Python. In any case, the code would likely fail naturally if it is not a list.

After cutting all that excess, you should drop the # Loop through elements comment as well.