input: Write a function called `format_text` that takes in a given piece of text, and optionally a font style, font size, and color as arguments. The function should return the formatted text wrapped in a HTML span tag with the specified styles applied. If no arguments for font, size, or color are provided, the function should use default values of 'Times New Roman', '14px', and '#000000' respectively.
  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('Text with new styles', font='Arial', size='18px', color='#FF0000')=='<span style="font-family: Arial" font-size: 18px color: #FF0000>Text with new styles</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 f'<span style="font-family: {font}; font-size: {size}; color: {color}">{text}</span>'