FEATURE: display PM participant group names in the topics list. (#21677)

After this change, we can view all participant group names on the topic list page.

Co-authored-by: Régis Hanol <regis@hanol.fr>

spec/lib/group_lookup_spec.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+RSpec.describe GroupLookup do
+  fab!(:group) { Fabricate(:group) }
+
+  describe "#[]" do
+    before { @group_lookup = GroupLookup.new([group.id, nil]) }
+
+    it "returns nil if group_id does not exists" do
+      expect(@group_lookup[0]).to eq(nil)
+    end
+
+    it "returns nil if group_id is nil" do
+      expect(@group_lookup[nil]).to eq(nil)
+    end
+
+    it "returns name if group_id exists" do
+      expect(@group_lookup[group.id]).to eq(group.name)
+    end
+  end
+end