### Question:
Federation { public List<UldECKey> getPublicKeys() { return publicKeys; } Federation(List<UldECKey> publicKeys, Instant creationTime, long creationBlockNumber,  NetworkParameters uldParams); List<UldECKey> getPublicKeys(); int getNumberOfSignaturesRequired(); Instant getCreationTime(); NetworkParameters getUldParams(); long getCreationBlockNumber(); Script getRedeemScript(); Script getP2SHScript(); Address getAddress(); int getSize(); Integer getPublicKeyIndex(UldECKey key); boolean hasPublicKey(UldECKey key); boolean hasMemberWithUscAddress(byte[] address); @Override String toString(); @Override boolean equals(Object other); @Override int hashCode();  }### Answer:
@Test public void publicKeysImmutable() { boolean exception = false; try { federation.getPublicKeys().add(UldECKey.fromPrivate(BigInteger.valueOf(1000))); } catch (Exception e) { exception = true; } Assert.assertTrue(exception); exception = false; try { federation.getPublicKeys().remove(0); } catch (Exception e) { exception = true; } Assert.assertTrue(exception); }