Regression test for irregular inflection on has_many

Also add a Changelog entry

[related #9702]
[fixes #8928]

activerecord/CHANGELOG.md

+*   Fixed has_many association to make it support irregular inflections.
+
+    Fixes #8928.
+
+    *arthurnn*, *Javier Goizueta*
+
 *   Fixed a problem where count used with a grouping was not returning a Hash.
 
     Fixes #14721.

activerecord/test/cases/reflection_test.rb

@@ -87,6 +87,14 @@ def test_reflection_klass_for_nested_class_name
     end
   end
 
+  def test_irregular_reflection_class_name
+    ActiveSupport::Inflector.inflections do |inflect|
+      inflect.irregular 'plural_irregular', 'plurales_irregulares'
+    end
+    reflection = AssociationReflection.new(:has_many, 'plurales_irregulares', nil, {}, ActiveRecord::Base)
+    assert_equal 'PluralIrregular', reflection.class_name
+  end
+
   def test_aggregation_reflection
     reflection_for_address = AggregateReflection.new(
       :composed_of, :address, nil, { :mapping => [ %w(address_street street), %w(address_city city), %w(address_country country) ] }, Customer