Use Encoding::UTF_8 constant for default_{internal,external} in the tests

actionmailer/test/abstract_unit.rb

@@ -3,8 +3,8 @@
 # These are the normal settings that will be set up by Railties
 # TODO: Have these tests support other combinations of these values
 silence_warnings do
-  Encoding.default_internal = "UTF-8"
-  Encoding.default_external = "UTF-8"
+  Encoding.default_internal = Encoding::UTF_8
+  Encoding.default_external = Encoding::UTF_8
 end
 
 module Rails

actionpack/test/abstract_unit.rb

@@ -7,8 +7,8 @@
 # These are the normal settings that will be set up by Railties
 # TODO: Have these tests support other combinations of these values
 silence_warnings do
-  Encoding.default_internal = "UTF-8"
-  Encoding.default_external = "UTF-8"
+  Encoding.default_internal = Encoding::UTF_8
+  Encoding.default_external = Encoding::UTF_8
 end
 
 require "drb"

actionview/test/abstract_unit.rb

@@ -9,8 +9,8 @@
 # These are the normal settings that will be set up by Railties
 # TODO: Have these tests support other combinations of these values
 silence_warnings do
-  Encoding.default_internal = "UTF-8"
-  Encoding.default_external = "UTF-8"
+  Encoding.default_internal = Encoding::UTF_8
+  Encoding.default_external = Encoding::UTF_8
 end
 
 require "active_support/testing/autorun"

activesupport/test/abstract_unit.rb

@@ -3,8 +3,8 @@
 require "active_support/core_ext/kernel/reporting"
 
 silence_warnings do
-  Encoding.default_internal = "UTF-8"
-  Encoding.default_external = "UTF-8"
+  Encoding.default_internal = Encoding::UTF_8
+  Encoding.default_external = Encoding::UTF_8
 end
 
 require "active_support/testing/autorun"