@Test
  public void testSetSigmaAndKey() {
    int[] key =
        TestUtil.twoCompInt(
            new long[] {
              0x03020100, 0x07060504, 0x0b0a0908, 0x0f0e0d0c,
              0x13121110, 0x17161514, 0x1b1a1918, 0x1f1e1d1c
            });
    int[] state = new int[ChaCha20Util.BLOCK_SIZE_IN_INTS];
    ChaCha20Util.setSigmaAndKey(state, key);
    // Verify that first four words equal ChaCha20Util.SIGMA.
    assertThat(Arrays.copyOf(state, 4))
        .isEqualTo(
            TestUtil.twoCompInt(new long[] {0x61707865, 0x3320646e, 0x79622d32, 0x6b206574}));
    // Verify that next eight words equal key.
    assertThat(Arrays.copyOfRange(state, 4, 12)).isEqualTo(key);
  }
https://datatracker.ietf.org/doc/html/rfc7539#section-2.3.2
java_src/src/test/java/com/google/crypto/tink/aead/internal/ChaCha20UtilTest.java