Handle `FrozenError` if it is available

This pull request handles `FrozenError` introduced by Ruby 2.5.
Refer https://bugs.ruby-lang.org/projects/ruby-trunk/repository/revisions/61131

Since `FrozenError` is a subclass of `RuntimeError` minitest used by master
branch can handle it, though it would be better to handle `FrozenError`
explicitly if possible.

`FrozenError` does not exist in Ruby 2.4 or lower, `frozen_error_class`
handles which exception is expected to be raised.

This pull request is intended to be merged to master,
then backported to `5-1-stable` to address #31508

2 files changed, 5 insertions, 1 deletions

diff --git a/railties/test/application/middleware_test.rb b/railties/test/application/middleware_test.rb
index 470a5326c6..d59384e982 100644
--- a/railties/test/application/middleware_test.rb
+++ b/railties/test/application/middleware_test.rb
@@ -249,7 +249,7 @@ module ApplicationTests
 
     test "can't change middleware after it's built" do
       boot!
-      assert_raise RuntimeError do
+      assert_raise frozen_error_class do
         app.config.middleware.use Rack::Config
       end
     end
diff --git a/railties/test/isolation/abstract_unit.rb b/railties/test/isolation/abstract_unit.rb
index 96c6f21395..0ca0de5e6f 100644
--- a/railties/test/isolation/abstract_unit.rb
+++ b/railties/test/isolation/abstract_unit.rb
@@ -406,6 +406,10 @@ class ActiveSupport::TestCase
   include TestHelpers::Rack
   include TestHelpers::Generation
   include ActiveSupport::Testing::Stream
+
+  def frozen_error_class
+    Object.const_defined?(:FrozenError) ? FrozenError : RuntimeError
+  end
 end
 
 # Create a scope and build a fixture rails app