@Test
  public void testQuarterRound16() {
    int[] x =
        TestUtil.twoCompInt(
            new long[] {
              0x879531e0, 0xc5ecf37d, 0x516461b1, 0xc9a62f8a,
              0x44c20ef3, 0x3390af7f, 0xd9fc690b, 0x2a5f714c,
              0x53372767, 0xb00a5631, 0x974c541a, 0x359e9963,
              0x5c971061, 0x3d631689, 0x2098d9d6, 0x91dbd320
            });
    ChaCha20Util.quarterRound(x, 2, 7, 8, 13);
    assertThat(x)
        .isEqualTo(
            TestUtil.twoCompInt(
                new long[] {
                  0x879531e0, 0xc5ecf37d, 0xbdb886dc, 0xc9a62f8a,
                  0x44c20ef3, 0x3390af7f, 0xd9fc690b, 0xcfacafd2,
                  0xe46bea80, 0xb00a5631, 0x974c541a, 0x359e9963,
                  0x5c971061, 0xccc07c79, 0x2098d9d6, 0x91dbd320
                }));
  }
https://tools.ietf.org/html/rfc7539#section-2.2.1
java_src/src/test/java/com/google/crypto/tink/aead/internal/ChaCha20UtilTest.java