diff --git a/test/mix/phoenix_test.exs b/test/mix/phoenix_test.exs
index cc2f976279..0d9121d8e5 100644
--- a/test/mix/phoenix_test.exs
+++ b/test/mix/phoenix_test.exs
@@ -3,6 +3,47 @@ defmodule Mix.PhoenixTest do
 
   doctest Mix.Phoenix, import: true
 
+  test "copy_from/4 uses file with .eex extension when it exists" do
+    tmp_dir = tmp_path!()
+    on_exit(fn -> File.rm_rf!(tmp_dir) end)
+
+    templates_dir = Path.join(tmp_dir, "templates")
+    File.mkdir_p!(templates_dir)
+    File.write!(Path.join(templates_dir, "hello.ex.eex"), "<%= greeting %>")
+    File.write!(Path.join(templates_dir, "hello.ex"), "old")
+
+    Mix.Phoenix.copy_from(
+      [tmp_dir],
+      "templates",
+      [greeting: "hi"],
+      [{:eex, "hello.ex.eex", Path.join(tmp_dir, "output.ex")}]
+    )
+
+    assert File.read!(Path.join(tmp_dir, "output.ex")) == "hi"
+  end
+
+  test "copy_from/4 falls back to file without .eex extension for backward compatibility" do
+    tmp_dir = tmp_path!()
+    on_exit(fn -> File.rm_rf!(tmp_dir) end)
+
+    templates_dir = Path.join(tmp_dir, "templates")
+    File.mkdir_p!(templates_dir)
+    File.write!(Path.join(templates_dir, "hello.ex"), "<%= greeting %>")
+
+    Mix.Phoenix.copy_from(
+      [tmp_dir],
+      "templates",
+      [greeting: "hi"],
+      [{:eex, "hello.ex.eex", Path.join(tmp_dir, "output.ex")}]
+    )
+
+    assert File.read!(Path.join(tmp_dir, "output.ex")) == "hi"
+  end
+
+  defp tmp_path! do
+    Path.join([System.tmp_dir!(), "phx_copy_from_test_#{System.unique_integer([:positive])}"])
+  end
+
   test "base/0 returns the module base based on the Mix application" do
     assert Mix.Phoenix.base() == "Phoenix"
     Application.put_env(:phoenix, :namespace, Phoenix.Sample.App)
diff --git a/test/mix/tasks/phx.gen.auth_test.exs b/test/mix/tasks/phx.gen.auth_test.exs
index 9c58980fd3..a16e11a3f9 100644
--- a/test/mix/tasks/phx.gen.auth_test.exs
+++ b/test/mix/tasks/phx.gen.auth_test.exs
@@ -1459,27 +1459,6 @@ defmodule Mix.Tasks.Phx.Gen.AuthTest do
     end)
   end
 
-  test "allows templates to be overridden (backwards compatibility)", config do
-    in_tmp_phx_project(config.test, fn ->
-      File.mkdir_p!("priv/templates/phx.gen.auth")
-      # verify that projects using the old filenames without .eex extension still work
-      File.write!("priv/templates/phx.gen.auth/auth.ex", "#it works with compat!")
-
-      send(self(), {:mix_shell_input, :yes?, false})
-
-      Gen.Auth.run(
-        ~w(Accounts Admin admins --no-compile),
-        ecto_adapter: Ecto.Adapters.Postgres
-      )
-
-      assert_received {:mix_shell, :yes?, [@liveview_option_message]}
-
-      assert_file("lib/my_app_web/admin_auth.ex", fn file ->
-        assert file =~ ~S|it works with compat!|
-      end)
-    end)
-  end
-
   test "with --no-agents-md does not inject content to AGENTS.md", config do
     in_tmp_phx_project(config.test, fn ->
       send(self(), {:mix_shell_input, :yes?, false})