Write a function to return the sum of all divisors of a number.
def sum_div(number):
    divisors = [1]
    for i in range(2, number):
        if (number % i)==0:
            divisors.append(i)
    return sum(divisors)
<s>[INST]<<SYS>>Given a task and its code, generate test cases for the code.<</SYS>>Write a function to return the sum of all divisors of a number.
def sum_div(number):
    divisors = [1]
    for i in range(2, number):
        if (number % i)==0:
            divisors.append(i)
    return sum(divisors)[/INST]assert sum_div(8)==7
assert sum_div(12)==16
assert sum_div(7)==1</s>