Program: 181084
Project: 181084
Buggy source:
@Override public boolean isValid(){
  boolean valid=true;
  Wall test=new WallImpl(new SquareImpl(tentative.topLeft().getCol(),tentative.topLeft().getRow()),tentative.getDirection());
  boolean direction=tentative.getDirection();
  if (direction == Wall.HORIZONTAL) {
    direction=Wall.VERTICAL;
  }
 else {
    direction=Wall.HORIZONTAL;
  }
  Wall opposite=new WallImpl(new SquareImpl(tentative.topLeft().getCol(),tentative.topLeft().getRow()),direction);
  if (setting.getPawn(owner,setting).getOwner().wallCount() <= 0) {
    valid=false;
  }
  if (tentative.topLeft().getCol() < 0) {
    valid=false;
  }
 else   if (tentative.topLeft().getRow() < 0) {
    valid=false;
  }
 else   if (tentative.topLeft().getCol() > 7) {
    valid=false;
  }
 else   if (tentative.topLeft().getRow() > 7) {
    valid=false;
  }
 else   if (setting.containsWall(test) == true) {
    valid=false;
  }
 else   if (setting.containsWall(opposite) == true) {
    valid=false;
  }
 else {
    setting.addWall(tentative);
    if (setting.pathToGoal(setting.getPawn(owner,setting)) == false) {
      valid=false;
    }
 else     if (setting.pathToGoal(setting.getPawn(owner.getOpponent(),setting)) == false) {
      valid=false;
    }
    setting.removeWall(tentative);
  }
  if (owner.hasWon(setting) || owner.getOpponent().hasWon(setting)) {
    valid=false;
  }
  return valid;
}

Fixed version (ground truth):
@Override public boolean isValid(){
  boolean valid=true;
  Wall test=new WallImpl(new SquareImpl(tentative.topLeft().getCol(),tentative.topLeft().getRow()),tentative.getDirection());
  Wall left=new WallImpl(new SquareImpl(tentative.topLeft().getCol() - 1,tentative.topLeft().getRow()),tentative.getDirection());
  Wall right=new WallImpl(new SquareImpl(tentative.topLeft().getCol() + 1,tentative.topLeft().getRow()),tentative.getDirection());
  boolean opDirection=tentative.getDirection();
  if (opDirection == Wall.HORIZONTAL) {
    opDirection=Wall.VERTICAL;
  }
 else {
    opDirection=Wall.HORIZONTAL;
  }
  Wall opposite=new WallImpl(new SquareImpl(tentative.topLeft().getCol(),tentative.topLeft().getRow()),opDirection);
  if (setting.getPawn(owner,setting).getOwner().wallCount() <= 0) {
    valid=false;
  }
  if (tentative.topLeft().getCol() < 0) {
    valid=false;
  }
 else   if (tentative.topLeft().getRow() < 0) {
    valid=false;
  }
 else   if (tentative.topLeft().getCol() > 7) {
    valid=false;
  }
 else   if (tentative.topLeft().getRow() > 7) {
    valid=false;
  }
 else   if (setting.containsWall(test) == true) {
    valid=false;
  }
 else   if (setting.containsWall(opposite) == true) {
    valid=false;
  }
 else   if (setting.containsWall(right) == true) {
    valid=false;
  }
 else   if (setting.containsWall(left) == true) {
    valid=false;
  }
 else {
    setting.addWall(tentative);
    if (setting.pathToGoal(setting.getPawn(owner,setting)) == false) {
      valid=false;
    }
 else     if (setting.pathToGoal(setting.getPawn(owner.getOpponent(),setting)) == false) {
      valid=false;
    }
    setting.removeWall(tentative);
  }
  if (owner.hasWon(setting) || owner.getOpponent().hasWon(setting)) {
    valid=false;
  }
  return valid;
}