实例变量在 rspec 中显示为“nil”

Question

我有以下测试代码：

require_relative '../spec_helper'

describe Chess::King do
  before do
    @piece = Chess::King.new('king1',:black)
    @board = Chess::Board.new
  end

  describe '#possible_moves' do
    context "placing king at location 4,5" do
      @board.grid[4][5] = @piece
      subject {@piece.possible_moves(@board)}
      it {is_expected.to eq([3,5],[3,6],[4,6],[5,6],[5,5])}
    end
  end
end

为什么会出现这个错误：

在block (3 levels) in <top (required)>': undefined methodgrid' 中为 nil:NilClass (NoMethodError)

我不确定这条线：@board.grid[4][5] = @piece。

我在这里的意图是将块对象分配给棋盘的网格实例变量（8x8数组）。

Answer 1

尝试改用let：

require_relative '../spec_helper'

describe Chess::King do
  let(:piece) { Chess::King.new('king1',:black) }
  let(:board) { Chess::Board.new }

  describe '#possible_moves' do
    context "placing king at location 4,5" do
      before(:each) { board.grid[4][5] = piece }
      subject {piece.possible_moves(board)}
      it {is_expected.to eq([3,5],[3,6],[4,6],[5,6],[5,5])}
    end
  end
end