Add failing diagnostic spec

ee/spec/graphql/mutations/design_management/upload_spec.rb

@@ -12,6 +12,11 @@ describe Mutations::DesignManagement::Upload do
     described_class.new(object: nil, context: { current_user: user }, field: nil)
   end
 
+  def run_mutation(fs = files)
+    mutation = described_class.new(object: nil, context: { current_user: user }, field: nil)
+    mutation.resolve(project_path: project.full_path, iid: issue.iid, files: fs)
+  end
+
   describe "#resolve" do
     let(:files) { [fixture_file_upload('spec/fixtures/dk.png')] }
 
@@ -34,6 +39,37 @@ describe Mutations::DesignManagement::Upload do
         enable_design_management
       end
 
+      describe 'contention in the design repo' do
+        let(:files) do
+          [
+            fixture_file_upload('spec/fixtures/dk.png'),
+            fixture_file_upload('spec/fixtures/rails_sample.jpg'),
+            fixture_file_upload('spec/fixtures/banana_sample.gif')
+          ].cycle(20).to_a
+        end
+
+        describe 'running requests in parallel' do
+          it 'does not cause errors' do
+            expect do
+              threads = files.map do |f|
+                Thread.new { run_mutation([f]) }
+              end
+              threads.each(&:join)
+            end.not_to raise_error
+          end
+        end
+
+        describe 'running requests in serial' do
+          it 'does not cause errors' do
+            expect do
+              files.each do |f|
+                run_mutation([f])
+              end
+            end.not_to raise_error
+          end
+        end
+      end
+
       context "when the user is not allowed to upload designs" do
         let(:user) { create(:user) }