input: Write a python function to generate a list of Fibonacci numbers less than 1000.
  assert generate_fibonacci() == [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987]
  assert generate_fibonacci()[-1] == 987
  assert len(generate_fibonacci()) == 17
output: def generate_fibonacci():
      fibonacci_list = []
      a, b = 0, 1
      while a < 1000:
          fibonacci_list.append(a)
          a, b = b, a + b
      return fibonacci_list