### Question:
Ed25519Utils { public static Ed25519EncodedFieldElement prepareForScalarMultiply(final PrivateKey key) { final byte[] hash = Hashes.sha512(key.getBytes()); final byte[] a = Arrays.copyOfRange(hash, 0, 32); a[31] &= 0x7F; a[31] |= 0x40; a[0] &= 0xF8; return new Ed25519EncodedFieldElement(a); } private  Ed25519Utils(); static Ed25519EncodedFieldElement prepareForScalarMultiply(final PrivateKey key);  }### Answer:
@Test public void prepareForScalarMultiplyReturnsClampedValue() { final PrivateKey privateKey = new PrivateKey(RandomUtils.generateRandomBytes(32)); final byte[] a = Ed25519Utils.prepareForScalarMultiply(privateKey).getRaw(); MatcherAssert.assertThat(a[31] & 0x40, IsEqual.equalTo(0x40)); MatcherAssert.assertThat(a[31] & 0x80, IsEqual.equalTo(0x0)); MatcherAssert.assertThat(a[0] & 0x7, IsEqual.equalTo(0x0)); }