private void assertBoardsSize(int size8, Chessboard chessboard, int expectedBoardsSize) {
        assertThat("all elements are not present on each board",
                chessboard.placeFiguresOnEmptyBoard()
                        .parallel()
                        .filter(board -> !board.contains(KING.getFigureAsString())
                                && board.contains(QUEEN.getFigureAsString())
                                && !board.contains(BISHOP.getFigureAsString())
                                && !board.contains(ROOK.getFigureAsString())
                                && !board.contains(KNIGHT.getFigureAsString())
                                && board.contains(FIELD_UNDER_ATTACK_STRING)
                                && leftOnlyFigures(board).length() == size8)
                        .map(e -> 1)
                        .reduce(0, (x, y) -> x + y), is(expectedBoardsSize));
    }