add more specs for Image Lightbox on Subfolder Install

spec/components/file_store/local_store_spec.rb

@@ -84,12 +84,22 @@ describe FileStore::LocalStore do
 
   end
 
+  def stub_for_subfolder
+    GlobalSetting.stubs(:relative_url_root).returns('/forum')
+    Discourse.stubs(:base_uri).returns("/forum")
+  end
+
   describe ".absolute_base_url" do
 
     it "is present" do
       expect(store.absolute_base_url).to eq("http://test.localhost/uploads/default")
     end
 
+    it "supports subfolder" do
+      stub_for_subfolder
+      expect(store.absolute_base_url).to eq("http://test.localhost/forum/uploads/default")
+    end
+
   end
 
   describe ".relative_base_url" do
@@ -98,6 +108,11 @@ describe FileStore::LocalStore do
       expect(store.relative_base_url).to eq("/uploads/default")
     end
 
+    it "supports subfolder" do
+      stub_for_subfolder
+      expect(store.relative_base_url).to eq("/forum/uploads/default")
+    end
+
   end
 
   it "is internal" do