add tests

mix.exs

@@ -6,6 +6,7 @@ defmodule FeedReader.MixProject do
       app: :feed_reader,
       version: "0.1.0",
       elixir: "~> 1.20.4",
+      elixirc_paths: elixirc_paths(Mix.env()),
       start_permanent: Mix.env() == :prod,
       aliases: aliases(),
       deps: deps()
@@ -20,6 +21,9 @@ defmodule FeedReader.MixProject do
     [preferred_envs: [precommit: :test]]
   end
 
+  defp elixirc_paths(:test), do: ["lib", "test/support"]
+  defp elixirc_paths(_), do: ["lib"]
+
   defp deps do
     [
       {:credo, "~> 1.7.19", only: :dev},