@Test
public void ecc25519HelperSignIsSideEffectFreeOnPrivateKeyParameter() {

    // ensure that clamping of pk2 is side-effect free.
    // the .clone() calls are to make sure no other side effects affect the outcome.
    final byte[] pk1 = KeyHolder.createPrivateKey("hello".getBytes());
    final byte[] pk2 = pk1.clone();

    byte[] sig = new Ecc25519Helper().sign("message".getBytes(), pk2, new KeyHolder(pk1.clone()).getPublicKeySignature());

    assertArrayEquals(pk1, pk2);
}