1describe World do
 2  subject { World.new(cells) }
 3  let(:cells) { [neighbor, other_cell] }
 4  let(:neighbor) { double }
 5  let(:other_cell) { double }
 6
 7  context "#neighbors_for" do
 8    let(:cell) { Cell.new }
 9
10    before :each do
11      cell.stub(:neighbor?).with(neighbor).and_return(true)
12      cell.stub(:neighbor?).with(other_cell).and_return(false)
13    end
14
15    it "returns the neighboring cells" do
16      expect(subject.neighbors_for(cell)).to include(neighbor)
17    end
18
19    it "does not return cells that are not neighbors" do
20      expect(subject.neighbors_for(cell)).to_not include(other_cell)
21    end
22  end
23
24  context "#next_generation!" do
25    subject { World.new([cell]) }
26    let(:cell) { double(spawn: true) }
27
28    it "visits each cell" do
29      subject.next_generation!
30      expect(cell).to have_received(:spawn).with(subject)
31    end
32  end
33
34  context "#empty?" do
35    context "when there are no living cells" do
36      it "returns true" do
37        neighbor.stub(:alive?).and_return(false)
38        other_cell.stub(:alive?).and_return(false)
39        expect(subject).to be_empty
40      end
41    end
42
43    context "when there is at least one living cell" do
44      it "returns false" do
45        neighbor.stub(:alive?).and_return(false)
46        other_cell.stub(:alive?).and_return(true)
47        expect(subject).to_not be_empty
48      end
49    end
50  end
51end