Extract shared RejectingPreferencesAdapter into test support

Credo Software Design flags the two identical RejectingAdapter
definitions in the controller and dispatcher tests as duplicate code
(mass 41). Move the adapter to `test/support/preferences/` and alias
it from both call sites.

Author: Flo0807

test/controllers/preferences_controller_test.exs

@@ -122,7 +122,7 @@ defmodule Backpex.PreferencesControllerTest do
       Application.put_env(:backpex, Backpex.Preferences,
         adapters: [
           {"ok.*", InMemory, []},
-          {"fail.*", Backpex.PreferencesControllerTest.RejectingAdapter, []},
+          {"fail.*", Backpex.Test.RejectingPreferencesAdapter, []},
           {:default, Backpex.Preferences.Adapters.Session, []}
         ]
       )
@@ -175,17 +175,4 @@ defmodule Backpex.PreferencesControllerTest do
     end
   end
 
-  defmodule RejectingAdapter do
-    @moduledoc false
-    @behaviour Backpex.Preferences.Adapter
-
-    @impl Backpex.Preferences.Adapter
-    def get(_ctx, _key, _opts), do: {:ok, :not_found}
-
-    @impl Backpex.Preferences.Adapter
-    def get_map(_ctx, _prefix, _opts), do: {:ok, %{}}
-
-    @impl Backpex.Preferences.Adapter
-    def put(_ctx, _key, _value, _opts), do: {:error, :rejected}
-  end
 end

test/preferences_test.exs

@@ -157,7 +157,7 @@ defmodule Backpex.PreferencesTest do
     end
 
     test "adapter returning {:error, reason} is surfaced to the caller" do
-      with_adapters([{:default, Backpex.PreferencesTest.RejectingAdapter, []}], fn ->
+      with_adapters([{:default, Backpex.Test.RejectingPreferencesAdapter, []}], fn ->
         conn = conn(:post, "/") |> Plug.Test.init_test_session(%{})
 
         log =
@@ -320,18 +320,6 @@ defmodule Backpex.PreferencesTest do
     def put(_ctx, _key, _value, _opts), do: raise("boom")
   end
 
-  defmodule RejectingAdapter do
-    @moduledoc false
-    @behaviour Backpex.Preferences.Adapter
-
-    @impl Backpex.Preferences.Adapter
-    def get(_ctx, _key, _opts), do: {:ok, :not_found}
-    @impl Backpex.Preferences.Adapter
-    def get_map(_ctx, _prefix, _opts), do: {:ok, %{}}
-    @impl Backpex.Preferences.Adapter
-    def put(_ctx, _key, _value, _opts), do: {:error, :rejected}
-  end
-
   defmodule UnidentifiedAdapter do
     @moduledoc false
     @behaviour Backpex.Preferences.Adapter

test/support/preferences/rejecting_adapter.ex

@@ -0,0 +1,20 @@
+defmodule Backpex.Test.RejectingPreferencesAdapter do
+  @moduledoc """
+  Test-only `Backpex.Preferences.Adapter` whose `put/4` always returns
+  `{:error, :rejected}`. Reads succeed as "not found."
+
+  Used to exercise the controller's error path and the dispatcher's
+  short-circuit semantics without having to wire a DB/stubbed adapter.
+  """
+
+  @behaviour Backpex.Preferences.Adapter
+
+  @impl Backpex.Preferences.Adapter
+  def get(_ctx, _key, _opts), do: {:ok, :not_found}
+
+  @impl Backpex.Preferences.Adapter
+  def get_map(_ctx, _prefix, _opts), do: {:ok, %{}}
+
+  @impl Backpex.Preferences.Adapter
+  def put(_ctx, _key, _value, _opts), do: {:error, :rejected}
+end