carrierwave: when migrating, create an empty blob if file is missing

spec/services/carrierwave_active_storage_migration_service_spec.rb

@@ -8,7 +8,7 @@ describe CarrierwaveActiveStorageMigrationService do
   end
 
   describe '.make_blob' do
-    let(:pj) { create(:piece_justificative, :rib) }
+    let(:pj) { create(:piece_justificative, :rib, updated_at: Time.zone.local(2019, 01, 01, 12, 00)) }
     let(:identify) { false }
 
     before do
@@ -17,6 +17,8 @@ describe CarrierwaveActiveStorageMigrationService do
 
     subject(:blob) { service.make_blob(pj.content, pj.updated_at.iso8601, filename: pj.original_filename, identify: identify) }
 
+    it { expect(blob.created_at).to eq pj.updated_at }
+
     it 'marks the blob as already scanned by the antivirus' do
       expect(blob.metadata[:virus_scan_result]).to eq(ActiveStorage::VirusScanner::SAFE)
     end
@@ -34,4 +36,37 @@ describe CarrierwaveActiveStorageMigrationService do
       end
     end
   end
+
+  describe '.make_empty_blob' do
+    let(:pj) { create(:piece_justificative, :rib, updated_at: Time.zone.local(2019, 01, 01, 12, 00)) }
+
+    before 'set the underlying stored file as missing' do
+      allow(pj.content.file).to receive(:file).and_return(nil)
+    end
+
+    subject(:blob) { service.make_empty_blob(pj.content, pj.updated_at.iso8601, filename: pj.original_filename) }
+
+    it { expect(blob.created_at).to eq pj.updated_at }
+
+    it 'marks the blob as already scanned by the antivirus' do
+      expect(blob.metadata[:virus_scan_result]).to eq(ActiveStorage::VirusScanner::SAFE)
+    end
+
+    it 'sets the blob MIME type from the file' do
+      expect(blob.identified).to be true
+      expect(blob.content_type).to eq 'application/pdf'
+    end
+
+    context 'when the file metadata are also missing' do
+      before do
+        allow(pj).to receive(:original_filename).and_return(nil)
+        allow(pj.content).to receive(:content_type).and_return(nil)
+      end
+
+      it 'fallbacks on default values' do
+        expect(blob.filename).to eq pj.content.filename
+        expect(blob.content_type).to eq 'text/plain'
+      end
+    end
+  end
 end