@barnabyalter anyway we can get some `contexts` in here?
I'm thinking

    context 'when the document field has more than one value' do
      ...
    end
    context 'when the document field has one value' do
      ...
    end
    context 'when the results are passed in' do
      it 'should append to them' do
        ...
      end
    end
    context 'when args are nil' do
      it 'should not raise an error' do
        ...
      end
      it { should be_nil }
    end