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/activesupport/test/abstract_unit.rb b/activesupport/test/abstract_unit.rb
index 3ac11e0fe0..f214898145 100644
--- a/activesupport/test/abstract_unit.rb
+++ b/activesupport/test/abstract_unit.rb
@@ -38,4 +38,8 @@ class ActiveSupport::TestCase
   private def jruby_skip(message = "")
     skip message if defined?(JRUBY_VERSION)
   end
+
+  def frozen_error_class
+    Object.const_defined?(:FrozenError) ? FrozenError : RuntimeError
+  end
 end
diff --git a/activesupport/test/core_ext/hash_ext_test.rb b/activesupport/test/core_ext/hash_ext_test.rb
index 746d7ad416..17952e9fc7 100644
--- a/activesupport/test/core_ext/hash_ext_test.rb
+++ b/activesupport/test/core_ext/hash_ext_test.rb
@@ -446,7 +446,7 @@ class HashExtTest < ActiveSupport::TestCase
     original.freeze
     assert_nothing_raised { original.except(:a) }
 
-    assert_raise(RuntimeError) { original.except!(:a) }
+    assert_raise(frozen_error_class) { original.except!(:a) }
   end
 
   def test_except_does_not_delete_values_in_original