An example of how I would answer the fibonacci question,

fibonacci.py

def fib(n):
    assert n > 0, "ERROR: n is less than 0!"
    if n == 0:
        return 1
    curr, prev, results = 1, 0, ['1']
    while n > 0:
        curr, prev = curr + prev, curr
        results.append(str(curr))
        n -= 1
    return ",".join(results)


def test_fib():
    try:
        fib(-1)
        print "ERROR! No error negative input"
    except AssertionError:
        pass
    assert(fib(1) == "1,1")
    assert(fib(2) == "1,1,2")
    assert(fib(3) == "1,1,2,3")

test_fib()