Write a python function to find the first even number in a given list of numbers.
def first_even(nums):
    first_even = next((el for el in nums if el%2==0),-1)
    return first_even
<s>[INST]<<SYS>>Given a task and its code, generate test cases for the code.<</SYS>>Write a python function to find the first even number in a given list of numbers.
def first_even(nums):
    first_even = next((el for el in nums if el%2==0),-1)
    return first_even[/INST]assert first_even ([1, 3, 5, 7, 4, 1, 6, 8]) == 4
assert first_even([2, 3, 4]) == 2
assert first_even([5, 6, 7]) == 6</s>