Support lowerCamel key format

test/unit/active_model/serializer/config_test.rb

@@ -67,6 +67,7 @@ module ActiveModel
         def test_apply_config_to_associations
           CONFIG.embed     = :ids
           CONFIG.embed_in_root = true
+          CONFIG.key_format = :lower_camel
 
           association = PostSerializer._associations[:comments]
           old_association = association.dup
@@ -76,6 +77,7 @@ module ActiveModel
           assert association.embed_ids?
           assert !association.embed_objects?
           assert association.embed_in_root
+          assert_equal :lower_camel, association.key_format
         ensure
           PostSerializer._associations[:comments] = old_association
           CONFIG.clear

test/unit/active_model/serializer/key_format_test.rb

@@ -0,0 +1,25 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class KeyFormatTest < Minitest::Test
+      def test_lower_camel_format_option
+        object     = Blog.new({ name: 'Name 1', display_name: 'Display Name 1'})
+        serializer = BlogSerializer.new(object, key_format: :lower_camel)
+
+        expected = { name: 'Name 1', displayName: 'Display Name 1' }
+
+        assert_equal expected, serializer.serializable_object
+      end
+
+      def test_lower_camel_format_serializer
+        object     = Blog.new({ name: 'Name 1', display_name: 'Display Name 1'})
+        serializer = BlogLowerCamelSerializer.new(object)
+
+        expected = { name: 'Name 1', displayName: 'Display Name 1' }
+
+        assert_equal expected, serializer.serializable_object
+      end
+    end
+  end
+end