Add a new feature flag remove_non_gma_memberships

This feature flag is to allow the release of GMAs without including
the side of effects or removing other groups or project memberships
while converting accounts to GMAs, which could be disruptive.

ee/app/services/group_saml/group_managed_accounts/transfer_membership_service.rb

@@ -51,9 +51,11 @@ module GroupSaml
       end
 
       def leave_non_gma_memberships
+        return true unless ::Feature.enabled?(:remove_non_gma_memberships)
+
         current_user.members.all? do |member|
           next true if member.source == group
-          next true if member.source.owner == current_user
+          next true if member.source.owned_by?(current_user)
 
           Members::DestroyService.new(current_user).execute(member)
           member.destroyed?

ee/spec/services/group_saml/group_managed_accounts/transfer_membership_service_spec.rb

@@ -11,7 +11,7 @@ describe GroupSaml::GroupManagedAccounts::TransferMembershipService do
   let(:session) { { 'oauth_data' => oauth_data } }
 
   before do
-    stub_feature_flags(convert_user_to_group_managed_accounts: true)
+    stub_feature_flags(convert_user_to_group_managed_accounts: true, remove_non_gma_memberships: false)
 
     allow(Gitlab::Auth::GroupSaml::IdentityLinker)
       .to receive(:new).with(current_user, oauth_data, session, group.saml_provider)
@@ -26,23 +26,57 @@ describe GroupSaml::GroupManagedAccounts::TransferMembershipService do
     expect(service.execute).to eq true
   end
 
-  it 'reduces the amount of memberships' do
+  it 'does not reduce the amount of memberships' do
     create(:project_member, :developer, user: current_user)
     create(:group_member, :developer, user: current_user)
 
-    expect { service.execute }.to change { current_user.members.count }.by(-2)
+    expect { service.execute }.not_to change { current_user.members.count }
   end
 
-  context 'when at least one non-owner member was not removed' do
+  context 'when remove_non_gma_memberships flag is enable' do
     before do
-      member = create(:group_member, :developer, user: current_user)
-      allow_next_instance_of(Members::DestroyService) do |service|
-        allow(service).to receive(:execute).with(member).and_return(member)
+      stub_feature_flags(remove_non_gma_memberships: true)
+    end
+
+    it 'reduces the amount of memberships' do
+      create(:project_member, :developer, user: current_user)
+      create(:group_member, :developer, user: current_user)
+
+      expect { service.execute }.to change { current_user.members.count }.by(-2)
+    end
+
+    context 'when at least one non-owner member was not removed' do
+      before do
+        member = create(:group_member, :developer, user: current_user)
+        allow_next_instance_of(Members::DestroyService) do |service|
+          allow(service).to receive(:execute).with(member).and_return(member)
+        end
+      end
+
+      it 'returns a falsy value' do
+        expect(service.execute).to be_falsy
       end
     end
 
-    it 'returns a falsy value' do
-      expect(service.execute).to be_falsy
+    context 'when the user changes are not saved' do
+      before do
+        allow(current_user).to receive(:save).and_return(false)
+      end
+
+      it "doesn't remove account's members" do
+        create(:group_member, :developer, user: current_user)
+
+        expect { service.execute }.not_to change { current_user.members.count }
+      end
+    end
+
+    context 'when the user is owner of a group' do
+      it 'does not reduce the amount of memberships' do
+        other_group = create(:group)
+        other_group.add_owner(current_user)
+
+        expect { service.execute }.not_to change { current_user.members.count }
+      end
     end
   end
 
@@ -51,12 +85,6 @@ describe GroupSaml::GroupManagedAccounts::TransferMembershipService do
       allow(current_user).to receive(:save).and_return(false)
     end
 
-    it "doesn't remove account's members" do
-      create(:group_member, :developer, user: current_user)
-
-      expect { service.execute }.not_to change { current_user.members.count }
-    end
-
     it "doesn't remove account's identities" do
       create(:identity, user: current_user)