refactor(DownloadManager): extract parallel download in dedicated class. move error management in custom class for procedure exports using the didicated class

spec/lib/download_manager/parallel_download_queue_spec.rb

@@ -0,0 +1,44 @@
+describe DownloadManager::ParallelDownloadQueue do
+  let(:test_dir) { Dir.mktmpdir(nil, Dir.tmpdir) }
+  let(:download_to_dir) { test_dir }
+  before do
+    downloadable_manager.on_error = proc { |_, _, _| }
+  end
+
+  after { FileUtils.remove_entry_secure(test_dir) if Dir.exist?(test_dir) }
+
+  let(:downloadable_manager) { DownloadManager::ParallelDownloadQueue.new([attachment], download_to_dir) }
+  describe '#download_one' do
+    subject { downloadable_manager.download_one(attachment: attachment, path_in_download_dir: destination, http_client: double) }
+
+    let(:destination) { 'lol.png' }
+    let(:attachment) do
+      PiecesJustificativesService::FakeAttachment.new(
+        file: StringIO.new('coucou'),
+        filename: "export-dossier.pdf",
+        name: 'pdf_export_for_instructeur',
+        id: 1,
+        created_at: Time.zone.now
+      )
+    end
+
+    context 'with a PiecesJustificativesService::FakeAttachment and it works' do
+      it 'write attachment.file to disk' do
+        target = File.join(download_to_dir, destination)
+        expect { subject }.to change { File.exist?(target) }
+        attachment.file.rewind
+        expect(attachment.file.read).to eq(File.read(target))
+      end
+    end
+
+    context 'with a PiecesJustificativesService::FakeAttachment and it fails' do
+      it 'write attachment.file to disk' do
+        expect(attachment.file).to receive(:read).and_raise("boom")
+        target = File.join(download_to_dir, destination)
+        expect { subject }.to raise_error(StandardError)
+        expect(File.exist?(target)).to be_falsey
+        # expect(downloadable_manager.errors).to have_key(destination)
+      end
+    end
+  end
+end