describe Imap::Backup::Downloader do
  describe "#run" do
    subject { described_class.new(folder, serializer) }

    let(:message) { {"RFC822" => "blah"} }
    let(:folder) do
      instance_double(
        Imap::Backup::Account::Folder,
        fetch: message,
        name: "folder"
      )
    end
    let(:folder_uids) { %w(111 222 333) }
    let(:serializer) do
      instance_double(Imap::Backup::Serializer::Mbox, save: nil)
    end
    let(:serializer_uids) { ["222"] }

    before do
      allow(folder).to receive(:uids).and_return(folder_uids)
      allow(serializer).to receive(:uids).and_return(serializer_uids)
      allow(folder).to receive(:fetch).with("333").and_return(nil)
      subject.run
    end

    context "#run" do
      context "fetched messages" do
        it "are saved" do
          expect(serializer).to have_received(:save).with("111", message)
        end
      end

      context "messages which are already present" do
        specify "are skipped" do
          expect(serializer).to_not have_received(:save).with("222", anything)
        end
      end

      context "failed fetches" do
        specify "are skipped" do
          expect(serializer).to_not have_received(:save).with("333", anything)
        end
      end
    end
  end
end