def METHOD_NAME(self):
    with fatfs.open(f"/{self._filename()}", "w") as f:
        f.write(bytearray(b"test" * 200))
    with fatfs.open(f"{self._filename()}", "a") as f:
        f.seek(800)
        f.write(bytearray(b"TEST" * 200))
    with fatfs.open(f"/{self._filename()}", "r") as f:
        b = bytearray(2000)
        r = f.read(b)
        self.assertEqual(r, 1600)
        self.assertEqual(bytes(b[:1600]), b"test" * 200 + b"TEST" * 200)