Tests that the end of flash ram on a atmega2560 is cleared by the bootloader on a new firmware upload.
There is a long known bug in a lot of mega2560 boot loaders that does not clear that flash above 0x3C000 This checks if your bootloader is effected by this or not.
AVR Fuse reading based on code found at https://www.avrfreaks.net/forum/read-fuse-bits-runtime by David Prentice
Example output consists of:
information:
"lockb = 0xFF" "ext fuse = 0xFD" "high fuse = 0xD8" "low fuse = 0xFF" "BOOT loader start : 0x3E000"
Now the code check that all high bytes are set to FF begins:
"Checking 0x3C000 through 0x3E000 has been cleared."
If the bytes are cleared you get a positive result
"This bootloader is good!"
If the bytes are not cleared you get, the first address that failed and its contents eg "Addr:3C000[1]" "This bootloader is faulty, it does not clear the full usable flash area"