Add test for user log_out user#destroy

spec/controllers/spree/user_sessions_controller_spec.rb

@@ -30,4 +30,13 @@ describe Spree::UserSessionsController, type: :controller do
       end
     end
   end
+
+  describe "destroy" do
+    it "redirects to root with flash message" do
+      spree_post :destroy
+  
+      expect(response).to redirect_to root_path
+      expect(flash[:notice]).to eq "Signed out successfully."
+    end
+  end
 end