Add tests

Signed-off-by: marcin mikołajczak <git@mkljczk.pl>

test/support/translation_mock.ex

@@ -0,0 +1,22 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2022 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule TranslationMock do
+  alias Pleroma.Translation.Service
+
+  @behaviour Service
+
+  @impl Service
+  def configured?, do: true
+
+  @impl Service
+  def translate(content, source_language, _target_language) do
+    {:ok,
+     %{
+       content: content |> String.reverse(),
+       detected_source_language: source_language,
+       provider: "TranslationMock"
+     }}
+  end
+end