Program: 181094
Project: 181094
Buggy source:
@Override public String toString(){
  String board="String_Node_Str";
  int pawn1Row=pawns._1().getSquare().getRow();
  int pawn1Col=pawns._1().getSquare().getCol();
  int pawn2Row=pawns._2().getSquare().getRow();
  int pawn2Col=pawns._2().getSquare().getCol();
  for (int i=0; i < 9; i++) {
    board+="String_Node_Str" + i + "String_Node_Str";
  }
  board+="String_Node_Str";
  for (  Wall w : walls) {
    System.out.println(w.topLeft().getRow());
    System.out.println(w.topLeft().getCol());
    System.out.println(w.getDirection());
  }
  if (wallBetween(new SquareImpl(3,4),new SquareImpl(4,4))) {
    System.out.println("String_Node_Str");
  }
  for (int i=0; i < 9 * 2 - 1; i++) {
    if (i % 2 == 0) {
      board+=i / 2 + "String_Node_Str";
    }
 else {
      board+="String_Node_Str";
    }
    for (int j=0; j < 9; j++) {
      if (wallBetween(new SquareImpl(j,i % 2),new SquareImpl(j + 1,i % 2)) == true) {
        System.out.println("String_Node_Str");
        board+="String_Node_Str";
      }
 else {
        board+="String_Node_Str";
      }
      if (i % 2 == 0) {
        if (pawn1Col == j && pawn1Row * 2 == i) {
          board+="String_Node_Str";
        }
 else         if (pawn2Col == j && pawn2Row * 2 == i) {
          board+="String_Node_Str";
        }
 else {
          board+="String_Node_Str";
        }
      }
 else {
        if (wallBetween(new SquareImpl(j,i % 2),new SquareImpl(j,i % 2 + 1)) == true) {
          board+="String_Node_Str";
        }
 else {
          board+="String_Node_Str";
        }
      }
    }
    board+="String_Node_Str";
  }
  board+="String_Node_Str";
  for (int i=0; i < 9; i++) {
    board+="String_Node_Str";
  }
  board+="String_Node_Str";
  return board;
}

Fixed version (ground truth):
@Override public String toString(){
  String board="String_Node_Str";
  int pawn1Row=pawns._1().getSquare().getRow();
  int pawn1Col=pawns._1().getSquare().getCol();
  int pawn2Row=pawns._2().getSquare().getRow();
  int pawn2Col=pawns._2().getSquare().getCol();
  for (int i=0; i < 9; i++) {
    board+="String_Node_Str" + i + "String_Node_Str";
  }
  board+="String_Node_Str";
  for (  Wall w : walls) {
    System.out.println(w.topLeft().getRow());
    System.out.println(w.topLeft().getCol());
    System.out.println(w.getDirection());
  }
  for (int i=0; i < 9 * 2 - 1; i++) {
    if (i % 2 == 0) {
      board+=i / 2 + "String_Node_Str";
    }
 else {
      board+="String_Node_Str";
    }
    for (int j=0; j < 9; j++) {
      if (wallBetween(new SquareImpl(j,i % 2),new SquareImpl(j + 1,i % 2)) == true) {
        System.out.println("String_Node_Str");
        board+="String_Node_Str";
      }
 else {
        board+="String_Node_Str";
      }
      if (i % 2 == 0) {
        if (pawn1Col == j && pawn1Row * 2 == i) {
          board+="String_Node_Str";
        }
 else         if (pawn2Col == j && pawn2Row * 2 == i) {
          board+="String_Node_Str";
        }
 else {
          board+="String_Node_Str";
        }
      }
 else {
        if (wallBetween(new SquareImpl(j,i % 2),new SquareImpl(j,i % 2 + 1)) == true) {
          board+="String_Node_Str";
        }
 else {
          board+="String_Node_Str";
        }
      }
    }
    board+="String_Node_Str";
  }
  board+="String_Node_Str";
  for (int i=0; i < 9; i++) {
    board+="String_Node_Str";
  }
  board+="String_Node_Str";
  return board;
}