old_contents: def check_nofiles(iso, filesize):
      assert(filesize == 1474560)
  
new_contents: def check_nofiles(fat, filesize):
      assert(filesize == 1474560)
      assert(fat.bytes_per_sector == 512)
      assert(fat.sectors_per_cluster == 1)
      assert(fat.reserved_sectors == 1)
      assert(fat.num_fats == 2)
      assert(fat.max_root_dir_entries == 224)
      assert(fat.sector_count == 2880)
      assert(fat.media == 0xf0)
      assert(fat.sectors_per_fat == 9)
      assert(fat.sectors_per_track == 18)
      assert(fat.num_heads == 2)
      assert(fat.hidden_sectors == 0)
      assert(fat.total_sector_count_32 == 0)
      assert(fat.drive_num == 0)
      assert(fat.boot_sig == 41)
      assert(fat.size_in_kb == 1440)
  
subject: Add in more checks.