input: Write a function to format a given piece of text with different options for font-style, size, and color. The function should return a formatted HTML string with the specified text style.
  
  def format_text(text, font="Times New Roman", size='14px', color='#000000'):
    return "<span style='font-family: {}; font-size: {}; color: {};'>{}</span>".format(font, size, color, text)
  
  assert format_text('Lorem ipsum dolor sit amet, consectetur adipiscing elit.', size='20px', color='#FF0000') == "<span style='font-family: Times New Roman; font-size: 20px; color: #FF0000;'>Lorem ipsum dolor sit amet, consectetur adipiscing elit.</span>"
  assert format_text('Suspendisse orci elit, lacinia at eleifend non, ullamcorper sed felis.', font='Arial', size='16px') == "<span style='font-family: Arial; font-size: 16px; color: #000000;'>Suspendisse orci elit, lacinia at eleifend non, ullamcorper sed felis.</span>"
  assert format_text('Mauris ut dui fermentum, tincidunt lorem et, posuere diam.', color='#0000FF') == "<span style='font-family: Times New Roman; font-size: 14px; color: #0000FF;'>Mauris ut dui fermentum, tincidunt lorem et, posuere diam.</span>"
  assert format_text('') == "<span style='font-family: Times New Roman; font-size: 14px; color: #000000;'></span>"
output: def format_text(text, font="Times New Roman", size='14px', color='#000000'):
    return "<span style='font-family: {}; font-size: {}; color: {};'>{}</span>".format(font, size, color, text)