You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: block.rs
    path of file: ./repos/phaser/phaser/vendor/ring/src/aead
    
    the code of the file until where you have to start completion: // Copyright 2018 Brian Smith.
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
// SPECIAL, DIRECT, INDIRE
    
    fn test_bitxor_assign() {
        const ONES: u64 = -1i64 as u64;
        const TEST_CASES: &[([u64; 2], [u64; 2], [u64; 2])] = &[
            ([0, 0], [0, 0], [0, 0]),
            ([0, 0], [ONES, ONES], [ONES, ONES]),
            ([0, ONES], [ONES, 0], [ONES, ONES]),
            ([ONES, 0], [0, ONES], [ONES, ONES]),
            ([ONES, ONES], [ONES, ONES], [0, 0]),
        ];
        for (expected_result, a, b) in TEST_CASES {
            let mut r = Block::from_u64_le(a[0].into(), a[1].into());
            r.bitxor_assign(Block::from_u64_le(b[0].into(), b[1].into()));
            assert_eq!(*expected_result, r.subblocks);

            // XOR is symmetric.
            let mut r = Block::from_u64_le(b[0].into(), b[1].into());
            r.bitxor_assign(Block::from_u64_le(a[0].into(), a[1].into()));
            assert_eq!(*expected_result, r.subblocks);
        }
    }