The equivalent of used "tr" command is .upper(), not .swapcase().

Instead of the loop

    for s in sys.stdin.read(): sys.stdout.write(s.upper())

you can write just

    sys.stdout.write(sys.stdin.read().upper())

But actually the loop is needed for testing purpose.

    while True:
        b = sys.stdin.buffer.read(1)
        if not b:
            break
        sys.stdout.buffer.write(b.upper())

And sys.executable should be escaped for the case of spaces or other special symbols in the path.

All this complicates tests too much. I prefer to skip some tests on Android.