input: Write a python function to generate a GDSII file with a specific cell arrangement and dimensions using the provided parameters.
  assert os.path.exists("wafer_mask.gds")
  assert isinstance(gdspy.GdsLibrary().read_gds('wafer_mask.gds'), gdspy.GdsLibrary)
output: import gdspy
  import os
  
  def create_gdsii_file():
      # Create a new GDSII library
      lib = gdspy.GdsLibrary()
  
      # Define a cell
      cell = lib.new_cell('WAFER')
  
      # Add a rectangle to the cell
      rect = gdspy.Rectangle((0, 0), (10, 10))
      cell.add(rect)
  
      # Write the GDSII file
      lib.write_gds('wafer_mask.gds')
  
  create_gdsii_file()