input: Write a function to format a given piece of text with different options for font-style, size, and color. The function should return the formatted text as a string with the specified styles applied. If no options are provided, default values should be used.
  assert format_text('Lorem ipsum dolor sit amet')=='<span style=\'font-family: Times New Roman\' font-size: 14px\' color: #000000\'>Lorem ipsum dolor sit amet</span>'
  assert format_text('Aliquam non velit sit amet arcu placerat vulputate a ut nibh.', font="Arial", size='12px', color='#FF0000')=='<span style=\'font-family: Arial\' font-size: 12px\' color: #FF0000\'>Aliquam non velit sit amet arcu placerat vulputate a ut nibh.</span>'
  assert format_text('Integer ut lectus vel nisi consequat bibendum ac a erat.', font="Verdana", size='16px')=='<span style=\'font-family: Verdana\' font-size: 16px\' color: #000000\'>Integer ut lectus vel nisi consequat bibendum ac a erat.</span>'
  assert format_text('')==''
  assert format_text('Lorem ipsum dolor sit amet')==''
output: def format_text(text, font="Times New Roman", size="14px", color="#000000"):
      if text == "":
          return ""
      return f"<span style='font-family: {font}' font-size: {size}' color: {color}'>{text}</span>"