diff --git a/.tool-versions b/.tool-versions
new file mode 100644
index 0000000..5c46c3b
--- /dev/null
+++ b/.tool-versions
@@ -0,0 +1,2 @@
+erlang 27.3.4.3
+elixir 1.18.4-otp-27
diff --git a/mix.exs b/mix.exs
index c9b752b..2e9b991 100644
--- a/mix.exs
+++ b/mix.exs
@@ -6,6 +6,7 @@ defmodule WebPushElixir.MixProject do
       app: :web_push_elixir,
       version: "0.4.0",
       elixir: "~> 1.15",
+      elixirc_paths: elixirc_paths(Mix.env()),
       start_permanent: Mix.env() == :prod,
       deps: deps(),
       description: "Simple web push for Elixir",
@@ -25,16 +26,20 @@ defmodule WebPushElixir.MixProject do
     ]
   end
 
+  # Specifies which paths to compile per environment.
+  defp elixirc_paths(:test), do: ["lib", "test/support"]
+  defp elixirc_paths(_), do: ["lib"]
+
   # Run "mix help deps" to learn about dependencies.
   defp deps do
     [
-      {:ex_doc, "~> 0.27", only: :dev, runtime: false},
-      {:excoveralls, "~> 0.10", only: :test},
       {:jose, "~> 1.11"},
       {:jason, "~> 1.4"},
-      {:plug, "~> 1.14"},
-      {:plug_cowboy, "~> 2.0"},
-      {:httpoison, "~> 2.0"}
+      {:httpoison, "~> 2.0"},
+      {:ex_doc, "~> 0.27", only: :dev, runtime: false},
+      {:excoveralls, "~> 0.10", only: :test},
+      {:plug, "~> 1.14", only: :test},
+      {:plug_cowboy, "~> 2.0", only: :test}
     ]
   end
 end
diff --git a/lib/web_push_elixir/mock_server.ex b/test/support/mock_server.ex
similarity index 100%
rename from lib/web_push_elixir/mock_server.ex
rename to test/support/mock_server.ex
diff --git a/test/test_helper.exs b/test/test_helper.exs
index 4983c7c..2f08246 100644
--- a/test/test_helper.exs
+++ b/test/test_helper.exs
@@ -1,3 +1,6 @@
 ExUnit.start()
 
-DynamicSupervisor.start_child(WebPushElixir.DynamicSupervisor,{Plug.Cowboy, scheme: :http, plug: WebPushElixir.MockServer, options: [port: 4040]})
+DynamicSupervisor.start_child(
+  WebPushElixir.DynamicSupervisor,
+  {Plug.Cowboy, scheme: :http, plug: WebPushElixir.MockServer, options: [port: 4040]}
+)
diff --git a/test/web_push_elixir_test.exs b/test/web_push_elixir_test.exs
index f4e0805..8c8b54d 100644
--- a/test/web_push_elixir_test.exs
+++ b/test/web_push_elixir_test.exs
@@ -1,7 +1,9 @@
 defmodule WebPushElixirTest do
   use ExUnit.Case
 
-  @subscription '{"endpoint":"http://localhost:4040/some-push-service","keys":{"p256dh":"BNcRdreALRFXTkOOUHK1EtK2wtaz5Ry4YfYCA_0QTpQtUbVlUls0VJXg7A8u-Ts1XbjhazAkj7I99e8QcYP7DkM=","auth":"tBHItJI5svbpez7KI4CCXg=="}}'
+  @subscription """
+  {"endpoint":"http://localhost:4040/some-push-service","keys":{"p256dh":"BNcRdreALRFXTkOOUHK1EtK2wtaz5Ry4YfYCA_0QTpQtUbVlUls0VJXg7A8u-Ts1XbjhazAkj7I99e8QcYP7DkM=","auth":"tBHItJI5svbpez7KI4CCXg=="}}
+  """
 
   test "it should send notification" do
     %{