3 files changed, 40 insertions, 0 deletions
diff --git a/activesupport/test/core_ext/string_ext_test.rb b/activesupport/test/core_ext/string_ext_test.rb
index 98bcdda45b..b0ebe0af8e 100644
--- a/activesupport/test/core_ext/string_ext_test.rb
+++ b/activesupport/test/core_ext/string_ext_test.rb
@@ -77,6 +77,12 @@ class StringInflectionsTest < ActiveSupport::TestCase
     end
   end
 
+  def test_titleize_with_keep_id_suffix
+    MixtureToTitleCaseWithKeepIdSuffix.each do |before, titleized|
+      assert_equal(titleized, before.titleize(keep_id_suffix: true))
+    end
+  end
+
   def test_upcase_first
     assert_equal "What a Lovely Day", "what a Lovely Day".upcase_first
   end
@@ -198,6 +204,12 @@ class StringInflectionsTest < ActiveSupport::TestCase
     end
   end
 
+  def test_humanize_with_keep_id_suffix
+    UnderscoreToHumanWithKeepIdSuffix.each do |underscore, human|
+      assert_equal(human, underscore.humanize(keep_id_suffix: true))
+    end
+  end
+
   def test_humanize_with_html_escape
     assert_equal "Hello", ERB::Util.html_escape("hello").humanize
   end
diff --git a/activesupport/test/inflector_test.rb b/activesupport/test/inflector_test.rb
index d881bd346d..4a3f64ef57 100644
--- a/activesupport/test/inflector_test.rb
+++ b/activesupport/test/inflector_test.rb
@@ -93,6 +93,13 @@ class InflectorTest < ActiveSupport::TestCase
     end
   end
 
+  MixtureToTitleCaseWithKeepIdSuffix.each_with_index do |(before, titleized), index|
+    define_method "test_titleize_with_keep_id_suffix_mixture_to_title_case_#{index}" do
+      assert_equal(titleized, ActiveSupport::Inflector.titleize(before, keep_id_suffix: true),
+        "mixture to TitleCase with keep_id_suffix failed for #{before}")
+    end
+  end
+
   def test_camelize
     CamelToUnderscore.each do |camel, underscore|
       assert_equal(camel, ActiveSupport::Inflector.camelize(underscore))
@@ -308,6 +315,12 @@ class InflectorTest < ActiveSupport::TestCase
     end
   end
 
+  def test_humanize_with_keep_id_suffix
+    UnderscoreToHumanWithKeepIdSuffix.each do |underscore, human|
+      assert_equal(human, ActiveSupport::Inflector.humanize(underscore, keep_id_suffix: true))
+    end
+  end
+
   def test_humanize_by_rule
     ActiveSupport::Inflector.inflections do |inflect|
       inflect.human(/_cnt$/i, '\1_count')
diff --git a/activesupport/test/inflector_test_cases.rb b/activesupport/test/inflector_test_cases.rb
index b660987d92..20a1c5b35d 100644
--- a/activesupport/test/inflector_test_cases.rb
+++ b/activesupport/test/inflector_test_cases.rb
@@ -248,12 +248,27 @@ module InflectorTestCases
     "_external_id"    => "External"
   }
 
+  UnderscoreToHumanWithKeepIdSuffix = {
+    "this_is_a_string_ending_with_id" => "This is a string ending with id",
+    "employee_id"                => "Employee id",
+    "employee_id_something_else" => "Employee id something else",
+    "underground"               => "Underground",
+    "_id"                       => "Id",
+    "_external_id"              => "External id"
+  }
+
   UnderscoreToHumanWithoutCapitalize = {
     "employee_salary" => "employee salary",
     "employee_id"     => "employee",
     "underground"     => "underground"
   }
 
+  MixtureToTitleCaseWithKeepIdSuffix = {
+    "this_is_a_string_ending_with_id" => "This Is A String Ending With Id",
+    "EmployeeId"                      => "Employee Id",
+    "Author Id"                       => "Author Id"
+  }
+
   MixtureToTitleCase = {
     "active_record"         => "Active Record",
     "ActiveRecord"          => "Active Record",