@Test
  public void testGeneratePrivateKeyReturnsIntentionallyMalformedKeys() {
    byte[] privateKey = X25519.generatePrivateKey();
    assertEquals(7, privateKey[0] & 7);
    assertEquals(128, privateKey[31] & 192);
  }
Tests against the test vectors in Section 6.1 of RFC 7748. https://tools.ietf.org/html/rfc7748
java_src/src/test/java/com/google/crypto/tink/subtle/X25519Test.java