it is changed in compile time

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

test/tasks/config_test.exs

@@ -0,0 +1,54 @@
+defmodule Mix.Tasks.Pleroma.ConfigTest do
+  use Pleroma.DataCase
+  alias Pleroma.Repo
+  alias Pleroma.Web.AdminAPI.Config
+
+  setup_all do
+    Mix.shell(Mix.Shell.Process)
+    temp_file = "config/temp.migrated.secret.exs"
+
+    dynamic = Pleroma.Config.get([:instance, :dynamic_configuration])
+
+    Pleroma.Config.put([:instance, :dynamic_configuration], true)
+
+    on_exit(fn ->
+      Mix.shell(Mix.Shell.IO)
+      Application.delete_env(:pleroma, :first_setting)
+      Application.delete_env(:pleroma, :second_setting)
+      Pleroma.Config.put([:instance, :dynamic_configuration], dynamic)
+      :ok = File.rm(temp_file)
+    end)
+
+    {:ok, temp_file: temp_file}
+  end
+
+  test "settings are migrated to db" do
+    assert Repo.all(Config) == []
+
+    Application.put_env(:pleroma, :first_setting, key: "value", key2: [Pleroma.Repo])
+    Application.put_env(:pleroma, :second_setting, key: "value2", key2: [Pleroma.Activity])
+
+    Mix.Tasks.Pleroma.Config.run(["migrate_to_db"])
+
+    first_db = Config.get_by_key("first_setting")
+    second_db = Config.get_by_key("second_setting")
+    refute Config.get_by_key("Pleroma.Repo")
+
+    assert Config.from_binary(first_db.value) == [key: "value", key2: [Pleroma.Repo]]
+    assert Config.from_binary(second_db.value) == [key: "value2", key2: [Pleroma.Activity]]
+  end
+
+  test "settings are migrated to file and deleted from db", %{temp_file: temp_file} do
+    Config.create(%{key: "setting_first", value: [key: "value", key2: [Pleroma.Activity]]})
+    Config.create(%{key: "setting_second", value: [key: "valu2", key2: [Pleroma.Repo]]})
+
+    Mix.Tasks.Pleroma.Config.run(["migrate_from_db", "temp"])
+
+    assert Repo.all(Config) == []
+    assert File.exists?(temp_file)
+    {:ok, file} = File.read(temp_file)
+
+    assert file =~ "config :pleroma, setting_first:"
+    assert file =~ "config :pleroma, setting_second:"
+  end
+end