1 files changed, 122 insertions, 0 deletions
diff --git a/spec/services/milestones/transfer_service_spec.rb b/spec/services/milestones/transfer_service_spec.rb
new file mode 100644
index 00000000000..b3d41eb0763
--- /dev/null
+++ b/spec/services/milestones/transfer_service_spec.rb
@@ -0,0 +1,122 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Milestones::TransferService do
+  describe '#execute' do
+    subject(:service) { described_class.new(user, old_group, project) }
+
+    context 'when old_group is present' do
+      let(:user) { create(:admin) }
+      let(:new_group) { create(:group) }
+      let(:old_group) { create(:group) }
+      let(:project) { create(:project, namespace: old_group) }
+      let(:group_milestone) { create(:milestone, group: old_group)}
+      let(:group_milestone2) { create(:milestone, group: old_group)}
+      let(:project_milestone) { create(:milestone, project: project)}
+      let!(:issue_with_group_milestone) { create(:issue, project: project, milestone: group_milestone) }
+      let!(:issue_with_project_milestone) { create(:issue, project: project, milestone: project_milestone) }
+      let!(:mr_with_group_milestone) { create(:merge_request, source_project: project, source_branch: 'branch-1', milestone: group_milestone) }
+      let!(:mr_with_project_milestone) { create(:merge_request, source_project: project, source_branch: 'branch-2', milestone: project_milestone) }
+
+      before do
+        new_group.add_maintainer(user)
+        project.add_maintainer(user)
+        # simulate project transfer
+        project.update(group: new_group)
+      end
+
+      context 'without existing milestone at the new group level' do
+        it 'recreates the missing group milestones at project level' do
+          expect { service.execute }.to change(project.milestones, :count).by(1)
+        end
+
+        it 'applies new project milestone to issues with group milestone' do
+          service.execute
+          new_milestone = issue_with_group_milestone.reload.milestone
+
+          expect(new_milestone).not_to eq(group_milestone)
+          expect(new_milestone.title).to eq(group_milestone.title)
+          expect(new_milestone.project_milestone?).to be_truthy
+        end
+
+        it 'does not apply new project milestone to issues with project milestone' do
+          service.execute
+
+          expect(issue_with_project_milestone.reload.milestone).to eq(project_milestone)
+        end
+
+        it 'applies new project milestone to merge_requests with group milestone' do
+          service.execute
+          new_milestone = mr_with_group_milestone.reload.milestone
+
+          expect(new_milestone).not_to eq(group_milestone)
+          expect(new_milestone.title).to eq(group_milestone.title)
+          expect(new_milestone.project_milestone?).to be_truthy
+        end
+
+        it 'does not apply new project milestone to issuables with project milestone' do
+          service.execute
+
+          expect(mr_with_project_milestone.reload.milestone).to eq(project_milestone)
+        end
+
+        it 'does not recreate missing group milestones that are not applied to issues or merge requests' do
+          service.execute
+          new_milestone_title = project.reload.milestones.pluck(:title)
+
+          expect(new_milestone_title).to include(group_milestone.title)
+          expect(new_milestone_title).not_to include(group_milestone2.title)
+        end
+
+        context 'when find_or_create_milestone returns nil' do
+          before do
+            allow_any_instance_of(Milestones::FindOrCreateService).to receive(:execute).and_return(nil)
+          end
+
+          it 'removes issues group milestone' do
+            service.execute
+
+            expect(mr_with_group_milestone.reload.milestone).to be_nil
+          end
+
+          it 'removes merge requests group milestone' do
+            service.execute
+
+            expect(issue_with_group_milestone.reload.milestone).to be_nil
+          end
+        end
+      end
+
+      context 'with existing milestone at the new group level' do
+        let!(:existing_milestone) { create(:milestone, group: new_group, title: group_milestone.title) }
+
+        it 'does not create a new milestone' do
+          expect { service.execute }.not_to change(project.milestones, :count)
+        end
+
+        it 'applies existing milestone to issues with group milestone' do
+          service.execute
+
+          expect(issue_with_group_milestone.reload.milestone).to eq(existing_milestone)
+        end
+
+        it 'applies existing milestone to merge_requests with group milestone' do
+          service.execute
+
+          expect(mr_with_group_milestone.reload.milestone).to eq(existing_milestone)
+        end
+      end
+    end
+  end
+
+  context 'when old_group is not present' do
+    let(:user)        { create(:admin) }
+    let(:old_group)   { project.group }
+    let(:project)     { create(:project, namespace: user.namespace) }
+
+    it 'returns nil' do
+      expect(described_class.new(user, old_group, project).execute).to be_nil
+    end
+  end
+end