1 files changed, 79 insertions, 0 deletions
diff --git a/spec/services/merge_requests/update_assignees_service_spec.rb b/spec/services/merge_requests/update_assignees_service_spec.rb
new file mode 100644
index 00000000000..de03aab5418
--- /dev/null
+++ b/spec/services/merge_requests/update_assignees_service_spec.rb
@@ -0,0 +1,79 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe MergeRequests::UpdateAssigneesService do
+  include AfterNextHelpers
+
+  let_it_be(:group) { create(:group, :public) }
+  let_it_be(:project) { create(:project, :private, :repository, group: group) }
+  let_it_be(:user) { create(:user) }
+  let_it_be(:user2) { create(:user) }
+  let_it_be(:user3) { create(:user) }
+
+  let_it_be_with_reload(:merge_request) do
+    create(:merge_request, :simple, :unique_branches,
+           title: 'Old title',
+           description: "FYI #{user2.to_reference}",
+           assignee_ids: [user3.id],
+           source_project: project,
+           author: create(:user))
+  end
+
+  before do
+    project.add_maintainer(user)
+    project.add_developer(user2)
+    project.add_developer(user3)
+  end
+
+  let(:service) { described_class.new(project, user, opts) }
+  let(:opts) { { assignee_ids: [user2.id] } }
+
+  describe 'execute' do
+    def update_merge_request
+      service.execute(merge_request)
+      merge_request.reload
+    end
+
+    context 'when the parameters are valid' do
+      it 'updates the MR, and queues the more expensive work for later' do
+        expect_next(MergeRequests::HandleAssigneesChangeService, project, user) do |service|
+          expect(service)
+            .to receive(:async_execute)
+            .with(merge_request, [user3], execute_hooks: true)
+        end
+
+        expect { update_merge_request }
+          .to change(merge_request, :assignees).to([user2])
+          .and change(merge_request, :updated_at)
+          .and change(merge_request, :updated_by).to(user)
+      end
+
+      it 'does not update the assignees if they do not have access' do
+        opts[:assignee_ids] = [create(:user).id]
+
+        expect { update_merge_request }.not_to change(merge_request, :assignee_ids)
+      end
+
+      it 'is more efficient than using the full update-service' do
+        allow_next(MergeRequests::HandleAssigneesChangeService, project, user) do |service|
+          expect(service)
+            .to receive(:async_execute)
+            .with(merge_request, [user3], execute_hooks: true)
+        end
+
+        other_mr = create(:merge_request, :simple, :unique_branches,
+                          title: merge_request.title,
+                          description: merge_request.description,
+                          assignee_ids: merge_request.assignee_ids,
+                          source_project: merge_request.project,
+                          author: merge_request.author)
+
+        update_service = ::MergeRequests::UpdateService.new(project, user, opts)
+
+        expect { service.execute(merge_request) }
+          .to issue_fewer_queries_than { update_service.execute(other_mr) }
+      end
+    end
+  end
+end