improves the reloading disabled error message

The original message from Zeitwerk is "can't reload, please call
loader.enable_reloading before setup (Zeitwerk::Error)", which is not
very informative for Rails programmers.

Rails should err with a message worded in terms of its interface.

1 files changed, 9 insertions, 0 deletions

diff --git a/railties/test/application/zeitwerk_integration_test.rb b/railties/test/application/zeitwerk_integration_test.rb
index b248459e47..40d06ee999 100644
--- a/railties/test/application/zeitwerk_integration_test.rb
+++ b/railties/test/application/zeitwerk_integration_test.rb
@@ -156,6 +156,15 @@ class ZeitwerkIntegrationTest < ActiveSupport::TestCase
     assert_not Rails.autoloaders.once.reloading_enabled?
   end
 
+  test "reloading raises if config.cache_classes is true" do
+    boot("production")
+
+    e = assert_raises(StandardError) do
+      deps.clear
+    end
+    assert_equal "reloading is disabled because config.cache_classes is true", e.message
+  end
+
   test "eager loading loads code in engines" do
     $test_blog_engine_eager_loaded = false