Add missing test file

test/livebook_web/controllers/endpoint_test.exs

@@ -0,0 +1,24 @@
+defmodule LivebookWeb.EndpointTest do
+  use LivebookWeb.ConnCase, async: true
+
+  test "delete cookies once they go over a certain limit", %{conn: conn} do
+    cookies =
+      Enum.map(1..5, &"c#{&1}=#{String.duplicate("a", 4096)}") ++
+        Enum.map(1..5, &"lb:#{&1}=#{String.duplicate("a", 4096)}")
+
+    assert [
+             "c1=;" <> _,
+             "c2=;" <> _,
+             "c3=;" <> _,
+             "c4=;" <> _,
+             "c5=;" <> _,
+             "lb:session" <> _,
+             "lb:user_data" <> _
+           ] =
+             conn
+             |> put_req_header("cookie", Enum.join(cookies, "; "))
+             |> get(~p"/")
+             |> get_resp_header("set-cookie")
+             |> Enum.sort()
+  end
+end