input: Write a python function to generate a list of Fibonacci numbers until 2000.
  assert fibonacci_until_2000() == [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597]
  assert fibonacci_until_2000() != [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584]
  assert len(fibonacci_until_2000()) == 18
output: def fibonacci_until_2000():
      fib_list = [0, 1]
      while True:
          next_fib = fib_list[-1] + fib_list[-2]
          if next_fib >= 2000:
              break
          fib_list.append(next_fib)
      return fib_list