it is changed in compile time

we can't change module attributes and endpoint settings in runtime

test/config/transfer_task_test.exs

@@ -0,0 +1,35 @@
+defmodule Pleroma.Config.TransferTaskTest do
+  use Pleroma.DataCase
+
+  setup do
+    dynamic = Pleroma.Config.get([:instance, :dynamic_configuration])
+
+    Pleroma.Config.put([:instance, :dynamic_configuration], true)
+
+    on_exit(fn ->
+      Pleroma.Config.put([:instance, :dynamic_configuration], dynamic)
+    end)
+  end
+
+  test "transfer config values from db to env" do
+    refute Application.get_env(:pleroma, :test_key)
+    Pleroma.Web.AdminAPI.Config.create(%{key: "test_key", value: [live: 2, com: 3]})
+
+    Pleroma.Config.TransferTask.start_link()
+
+    assert Application.get_env(:pleroma, :test_key) == [live: 2, com: 3]
+
+    on_exit(fn ->
+      Application.delete_env(:pleroma, :test_key)
+    end)
+  end
+
+  test "non existing atom" do
+    Pleroma.Web.AdminAPI.Config.create(%{key: "undefined_atom_key", value: [live: 2, com: 3]})
+
+    assert ExUnit.CaptureLog.capture_log(fn ->
+             Pleroma.Config.TransferTask.start_link()
+           end) =~
+             "updating env causes error, key: \"undefined_atom_key\", error: %ArgumentError{message: \"argument error\"}"
+  end
+end