input: Write a python function to create a simple HTTP server using the socket module.
  assert start_server(8888) == "Server started on port 8888"
  assert start_server(9999) == "Server started on port 9999"
  assert start_server(8080) == "Server started on port 8080"
output: import socket
  
  def start_server(port):
      server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
      server_socket.bind(('', port))
      server_socket.listen(1)
      return f"Server started on port {port}"