public static boolean isFixedDifficultyInConfig(final GenesisConfigOptions config) {
    return config.getEthashConfigOptions().getFixedDifficulty().isPresent();
  }
This provides a difficulty calculator that can be used during development efforts; given
development (typically) uses CPU based mining, a negligible difficulty ensures tests etc. execute
quickly.
ethereum/core/src/main/java/org/hyperledger/besu/ethereum/difficulty/fixed/FixedDifficultyCalculators.java