input: Write a python function to generate a list of unique random numbers within a specified range.
  assert len(generate_random_numbers(5))==5
  assert len(set(generate_random_numbers(10)))==10
  assert all(isinstance(n, int) for n in generate_random_numbers(8))
output: import random
  
  def generate_random_numbers(n, start=0, end=100):
      if end - start + 1 < n:
          raise ValueError("Range is too small to generate the required number of unique numbers.")
      return random.sample(range(start, end + 1), n)