input: Write a function to format a given piece of text with different options for font-style, size, and color. If the given text is empty, return an empty string.
  def format_text(text, font="Times New Roman", size='14px', color='#000000'):
    if text == "":
      return ""
    return "<span style='font-family: {}; font-size: {}; color: {};'>{}</span>".format(font, size, color, text)
  
  assert format_text('Lorem ipsum dolor sit amet', 'Arial', '16px', '#FF0000')=='<span style='font-family: Arial; font-size: 16px; color: #FF0000;'>Lorem ipsum dolor sit amet</span>'
  assert format_text('')==''
  assert format_text('Hello World', 'Courier New', '20px', '#00FF00')=='<span style='font-family: Courier New; font-size: 20px; color: #00FF00;'>Hello World</span>'
  assert format_text('Test', 'Georgia', '24px', '#0000FF')=='<span style='font-family: Georgia; font-size: 24px; color: #0000FF;'>Test</span>'
  assert format_text('This is a sample text', 'Verdana', '12px', '#808080')=='<span style='font-family: Verdana; font-size: 12px; color: #808080;'>This is a sample text</span>'
output: def format_text(text, font="Times New Roman", size='14px', color='#000000'):
    if text == "":
      return ""
    return "<span style='font-family: {}; font-size: {}; color: {};'>{}</span>".format(font, size, color, text)