Require Ruby 2.5 for Rails 6.

Generally followed the pattern for https://github.com/rails/rails/pull/32034

* Removes needless CI configs for 2.4
* Targets 2.5 in rubocop
* Updates existing CHANGELOG entries for fewer merge conflicts
* Removes Hash#slice extension as that's inlined on Ruby 2.5.
* Removes the need for send on define_method in MethodCallAssertions.

1 files changed, 6 insertions, 8 deletions

diff --git a/activesupport/lib/active_support/testing/method_call_assertions.rb b/activesupport/lib/active_support/testing/method_call_assertions.rb
index eba41aa907..03c38be481 100644
--- a/activesupport/lib/active_support/testing/method_call_assertions.rb
+++ b/activesupport/lib/active_support/testing/method_call_assertions.rb
@@ -35,18 +35,16 @@ module ActiveSupport
           assert_called(object, method_name, message, times: 0, &block)
         end
 
-        # TODO: No need to resort to #send once support for Ruby 2.4 is
-        # dropped.
         def assert_called_on_instance_of(klass, method_name, message = nil, times: 1, returns: nil)
           times_called = 0
-          klass.send(:define_method, "stubbed_#{method_name}") do |*|
+          klass.define_method("stubbed_#{method_name}") do |*|
             times_called += 1
 
             returns
           end
 
-          klass.send(:alias_method, "original_#{method_name}", method_name)
-          klass.send(:alias_method, method_name, "stubbed_#{method_name}")
+          klass.alias_method "original_#{method_name}", method_name
+          klass.alias_method method_name, "stubbed_#{method_name}"
 
           yield
 
@@ -55,9 +53,9 @@ module ActiveSupport
 
           assert_equal times, times_called, error
         ensure
-          klass.send(:alias_method, method_name, "original_#{method_name}")
-          klass.send(:undef_method, "original_#{method_name}")
-          klass.send(:undef_method, "stubbed_#{method_name}")
+          klass.alias_method method_name, "original_#{method_name}"
+          klass.undef_method "original_#{method_name}"
+          klass.undef_method "stubbed_#{method_name}"
         end
 
         def assert_not_called_on_instance_of(klass, method_name, message = nil, &block)