@BeforeClass
  public static void generateKeyMaterial() throws GeneralSecurityException {
    privateKeyBytes = X25519.generatePrivateKey();
    publicKeyBytes = X25519.publicFromPrivate(privateKeyBytes);
  }
Unit tests for {@link HpkeEncrypt} and {@link HpkeDecrypt}.
java_src/src/test/java/com/google/crypto/tink/hybrid/internal/HpkeEncryptDecryptTest.java