Program: 159257
Project: 159257
Buggy source:
/** 
 * In case the choice of mana to be produced is obvious, let's discard all other abilities. Example: Pay {W}{R} Land produces {W} or {G}. No need to ask what player wants to choose. {W} mana ability should be left only. But we CAN do auto choice only in case we have basic mana abilities. Example: we should pay {1} and we have Cavern of Souls that can produce {1} or any mana of creature type choice. We can't simply auto choose {1} as the second mana ability also makes spell uncounterable. In case we can't auto choose we'll simply return the useableAbilities map back to caller without any modification.
 * @param unpaid Mana we need to pay. Can be null (it is for X costs now).
 * @param useableAbilities List of mana abilities permanent may produce
 * @return List of mana abilities permanent may produce and are reasonable for unpaid mana
 */
public static LinkedHashMap<UUID,ManaAbility> tryToAutoPay(ManaCost unpaid,LinkedHashMap<UUID,ManaAbility> useableAbilities){
  if (unpaid != null) {
    Mana mana=unpaid.getMana();
    for (    ManaAbility ability : useableAbilities.values()) {
      if (!(ability instanceof BasicManaAbility)) {
        return useableAbilities;
      }
    }
    int countColorfull=0;
    int countColorless=0;
    ManaAbility chosenManaAbility=null;
    for (    ManaAbility ability : useableAbilities.values()) {
      if (ability instanceof RedManaAbility && mana.contains(Mana.RedMana)) {
        chosenManaAbility=ability;
        countColorfull++;
      }
      if (ability instanceof BlackManaAbility && mana.contains(Mana.BlackMana)) {
        chosenManaAbility=ability;
        countColorfull++;
      }
      if (ability instanceof BlueManaAbility && mana.contains(Mana.BlueMana)) {
        chosenManaAbility=ability;
        countColorfull++;
      }
      if (ability instanceof WhiteManaAbility && mana.contains(Mana.WhiteMana)) {
        chosenManaAbility=ability;
        countColorfull++;
      }
      if (ability instanceof GreenManaAbility && mana.contains(Mana.GreenMana)) {
        chosenManaAbility=ability;
        countColorfull++;
      }
    }
    if (countColorfull == 0) {
      if (mana.getColorless() > 0) {
        return replace(useableAbilities,useableAbilities.values().iterator().next());
      }
      return useableAbilities;
    }
    if (countColorfull > 1) {
      return useableAbilities;
    }
    return replace(useableAbilities,chosenManaAbility);
  }
  return useableAbilities;
}

Fixed version (ground truth):
/** 
 * In case the choice of mana to be produced is obvious, let's discard all other abilities. Example: Pay {W}{R} Land produces {W} or {G}. No need to ask what player wants to choose. {W} mana ability should be left only. But we CAN do auto choice only in case we have basic mana abilities. Example: we should pay {1} and we have Cavern of Souls that can produce {1} or any mana of creature type choice. We can't simply auto choose {1} as the second mana ability also makes spell uncounterable. In case we can't auto choose we'll simply return the useableAbilities map back to caller without any modification.
 * @param unpaid Mana we need to pay. Can be null (it is for X costs now).
 * @param useableAbilities List of mana abilities permanent may produce
 * @return List of mana abilities permanent may produce and are reasonable for unpaid mana
 */
public static LinkedHashMap<UUID,ManaAbility> tryToAutoPay(ManaCost unpaid,LinkedHashMap<UUID,ManaAbility> useableAbilities){
  for (  ManaAbility ability : useableAbilities.values()) {
    if (!(ability instanceof BasicManaAbility)) {
      return useableAbilities;
    }
  }
  if (unpaid != null) {
    ManaSymbols symbols=ManaSymbols.buildFromManaCost(unpaid);
    Mana unpaidMana=unpaid.getMana();
    if (!symbols.isEmpty()) {
      return getManaAbilitiesUsingManaSymbols(useableAbilities,symbols,unpaidMana);
    }
 else {
      return getManaAbilitiesUsingMana(unpaid,useableAbilities);
    }
  }
  return useableAbilities;
}