stack_spec.rb

describe SymbolStack do
  context 'when stack is empty' do
    its (:size) { should eq 0 }

    describe 'SymbolStack#push' do
      context 'with symbol' do
        it 'increments stack size' do
          expect { subject.push(:data) }.
            to change { subject.size }.from(0).to(1)
        end
      end

      context 'with non-symbol' do
        it { expect { subject.push('data') }.to raise_error }
      end
    end

    describe 'SymbolStack#pop' do
      it { expect { subject.pop }.to raise_error }
    end
  end

  context 'when stack is full' do
    before do
      10.times {|i| subject.push(:"data#{i}") }
    end

    its (:size) { should eq 10 }

    describe 'SymbolStack#push' do
      context 'with symbol' do
        it { expect { subject.push(:data) }.to raise_error }
      end

      context 'with non-symbol' do
        it { expect { subject.push('data') }.to raise_error }
      end
    end

    describe 'SymbolStack#pop' do
      it 'returns top' do
        subject.pop.should eq :data9
      end
    end
  end

  context 'when stack is not empty or full' do
    before do
      subject.push(:data)
    end

    describe 'SymbolStack#push' do
      context 'with symbol' do
        it 'increments stack size' do
          expect { subject.push(:data) }.
            to change { subject.size }.from(1).to(2)
        end
      end

      context 'with non-symbol' do
        it { expect { subject.push('data') }.to raise_error }
      end
    end

    describe 'SymbolStack#pop' do
      it 'returns top' do
        subject.pop.should eq :data
      end
    end
  end

end