### Question:
ProofOfWorkValidationRule implements DetachedBlockHeaderValidationRule { @Override public boolean validate(final BlockHeader header, final BlockHeader parent) { if (includeBaseFee) { if (!ExperimentalEIPs.eip1559Enabled) { LOG.warn("Invalid block header: EIP-1559 feature flag must be enabled --Xeip1559-enabled"); return false; } else if (header.getBaseFee().isEmpty()) { LOG.warn("Invalid block header: missing mandatory base fee."); return false; } } final byte[] hashBuffer = new byte[64]; final Hash headerHash = hashHeader(header); HASHER.hash(hashBuffer, header.getNonce(), header.getNumber(), headerHash.toArray()); if (header.getDifficulty().isZero()) { LOG.trace("Rejecting header because difficulty is 0"); return false; } final BigInteger difficulty = header.getDifficulty().toBytes().toUnsignedBigInteger(); final UInt256 target = difficulty.equals(BigInteger.ONE) ? UInt256.MAX_VALUE : UInt256.valueOf(ETHASH_TARGET_UPPER_BOUND.divide(difficulty)); final UInt256 result = UInt256.fromBytes(Bytes32.wrap(hashBuffer, 32)); if (result.compareTo(target) > 0) { LOG.warn( "Invalid block header: the EthHash result {} was greater than the target {}.\n" + "Failing header:\n{}", result, target, header); return false; } final Hash mixedHash = Hash.wrap(Bytes32.leftPad(Bytes.wrap(hashBuffer).slice(0, Bytes32.SIZE))); if (!header.getMixHash().equals(mixedHash)) { LOG.warn( "Invalid block header: header mixed hash {} does not equal calculated mixed hash {}.\n" + "Failing header:\n{}", header.getMixHash(), mixedHash, header); return false; } return true; } ProofOfWorkValidationRule();  ProofOfWorkValidationRule(final boolean includeBaseFee); @Override boolean validate(final BlockHeader header, final BlockHeader parent); @Override boolean includeInLightValidation();  }### Answer:
@Test public void validatesValidBlocks() { assertThat(validationRule.validate(blockHeader, parentHeader)).isTrue(); }
@Test public void failsBlockWithZeroValuedDifficulty() { final BlockHeader header = BlockHeaderBuilder.fromHeader(blockHeader) .difficulty(Difficulty.ZERO) .blockHeaderFunctions(mainnetBlockHashFunction()) .buildBlockHeader(); assertThat(validationRule.validate(header, parentHeader)).isFalse(); }
@Test public void failsWithVeryLargeDifficulty() { final Difficulty largeDifficulty = Difficulty.of(BigInteger.valueOf(2).pow(255)); final BlockHeader header = BlockHeaderBuilder.fromHeader(blockHeader) .difficulty(largeDifficulty) .blockHeaderFunctions(mainnetBlockHashFunction()) .buildBlockHeader(); assertThat(validationRule.validate(header, parentHeader)).isFalse(); }
@Test public void failsWithMisMatchedMixHash() { final Hash updateMixHash = Hash.wrap(UInt256.fromBytes(blockHeader.getMixHash()).subtract(1L).toBytes()); final BlockHeader header = BlockHeaderBuilder.fromHeader(blockHeader) .mixHash(updateMixHash) .blockHeaderFunctions(mainnetBlockHashFunction()) .buildBlockHeader(); assertThat(validationRule.validate(header, parentHeader)).isFalse(); }
@Test public void failsWithMisMatchedNonce() { final long updatedNonce = blockHeader.getNonce() + 1; final BlockHeader header = BlockHeaderBuilder.fromHeader(blockHeader) .nonce(updatedNonce) .blockHeaderFunctions(mainnetBlockHashFunction()) .buildBlockHeader(); assertThat(validationRule.validate(header, parentHeader)).isFalse(); }