Question: 
Write a function to calculate the geometric sum of n-1.


Model's Code:
def geometric_sum(n):
    if n <= 0:
        return 0
    return 1 - (0.5 ** n)



Sample Correct Code:
def geometric_sum(n):
  if n < 0:
    return 0
  else:
    return 1 / (pow(2, n)) + geometric_sum(n - 1)


Asserts:
assert geometric_sum(7) == 1.9921875
assert geometric_sum(4) == 1.9375
assert geometric_sum(8) == 1.99609375


Tests:
Test 1 of 3: FAIL: AssertionError()

Test 738 of 974: 559/738 (75.74525745257452%): failed