diff --git a/actionmailer/lib/action_mailer/test_case.rb b/actionmailer/lib/action_mailer/test_case.rb
index 97afd87840e5b..1a07d8e79242e 100644
--- a/actionmailer/lib/action_mailer/test_case.rb
+++ b/actionmailer/lib/action_mailer/test_case.rb
@@ -74,6 +74,15 @@ def determine_default_mailer(name)
         end
       end
 
+      # Reads the fixture file for the given mailer.
+      #
+      # This is useful when testing mailers by being able to write the body of
+      # an email inside a fixture. See the testing guide for a concrete example:
+      # https://guides.rubyonrails.org/testing.html#revenge-of-the-fixtures
+      def read_fixture(action)
+        IO.readlines(File.join(Rails.root, "test", "fixtures", self.class.mailer_class.name.underscore, action))
+      end
+
       private
         def initialize_test_deliveries
           set_delivery_method :test
@@ -110,10 +119,6 @@ def charset
         def encode(subject)
           Mail::Encodings.q_value_encode(subject, charset)
         end
-
-        def read_fixture(action)
-          IO.readlines(File.join(Rails.root, "test", "fixtures", self.class.mailer_class.name.underscore, action))
-        end
     end
 
     include Behavior
diff --git a/activerecord/lib/active_record/fixtures.rb b/activerecord/lib/active_record/fixtures.rb
index 444d95a6b3627..69b2181fd4a3f 100644
--- a/activerecord/lib/active_record/fixtures.rb
+++ b/activerecord/lib/active_record/fixtures.rb
@@ -19,10 +19,13 @@ class FixtureClassNotFound < ActiveRecord::ActiveRecordError # :nodoc:
   #
   # \Fixtures are a way of organizing data that you want to test against; in short, sample data.
   #
-  # They are stored in YAML files, one file per model, which are placed in the directories
-  # appointed by <tt>ActiveSupport::TestCase.fixture_paths=(path)</tt> (this is automatically
-  # configured for Rails, so you can just put your files in <tt><your-rails-app>/test/fixtures/</tt>,
-  # or in the <tt>test/fixtures</tt> folder under any of your application's engines).
+  # They are stored in YAML files, one file per model, which are by default placed in either
+  # <tt><your-rails-app>/test/fixtures/</tt> or in the <tt>test/fixtures</tt>
+  # folder under any of your application's engines.
+  #
+  # The location can also be changed with ActiveSupport::TestCase.fixture_paths=,
+  # once you have <tt>require "rails/test_help"</tt> in your +test_helper.rb+.
+  #
   # The fixture file ends with the +.yml+ file extension, for example:
   # <tt><your-rails-app>/test/fixtures/web_sites.yml</tt>).
   #
@@ -42,10 +45,17 @@ class FixtureClassNotFound < ActiveRecord::ActiveRecordError # :nodoc:
   # is followed by an indented list of key/value pairs in the "key: value" format. Records are
   # separated by a blank line for your viewing pleasure.
   #
-  # Note: Fixtures are unordered. If you want ordered fixtures, use the omap YAML type.
-  # See https://yaml.org/type/omap.html
-  # for the specification. You will need ordered fixtures when you have foreign key constraints
-  # on keys in the same table. This is commonly needed for tree structures. Example:
+  # == Ordering
+  #
+  # Fixtures by default are unordered. This is because the maps in YAML are unordered.
+  #
+  # If you want ordered fixtures, use the omap YAML type.
+  # See https://yaml.org/type/omap.html for the specification.
+  #
+  # You will need ordered fixtures when you have foreign key constraints
+  # on keys in the same table. This is commonly needed for tree structures.
+  #
+  # For example:
   #
   #    --- !omap
   #    - parent:
@@ -57,7 +67,7 @@ class FixtureClassNotFound < ActiveRecord::ActiveRecordError # :nodoc:
   #        parent_id:  1
   #        title:      Child
   #
-  # = Using Fixtures in Test Cases
+  # == Using Fixtures in Test Cases
   #
   # Since fixtures are a testing construct, we use them in our unit and functional tests. There
   # are two ways to use the fixtures, but first let's take a look at a sample unit test:
@@ -127,7 +137,7 @@ class FixtureClassNotFound < ActiveRecord::ActiveRecordError # :nodoc:
   # traversed in the database to create the fixture hash and/or instance variables. This is expensive for
   # large sets of fixtured data.
   #
-  # = Dynamic fixtures with ERB
+  # == Dynamic fixtures with \ERB
   #
   # Sometimes you don't care about the content of the fixtures as much as you care about the volume.
   # In these cases, you can mix ERB in with your YAML fixtures to create a bunch of fixtures for load
@@ -165,7 +175,7 @@ class FixtureClassNotFound < ActiveRecord::ActiveRecordError # :nodoc:
   #       name: kitten.png
   #       sha: <%= file_sha 'files/kitten.png' %>
   #
-  # = Transactional Tests
+  # == Transactional Tests
   #
   # Test cases can use begin+rollback to isolate their changes to the database instead of having to
   # delete+insert for every test case.
@@ -201,7 +211,7 @@ class FixtureClassNotFound < ActiveRecord::ActiveRecordError # :nodoc:
   # 2. Your database does not support transactions. Every Active Record database supports transactions except MySQL MyISAM.
   #    Use InnoDB, MaxDB, or NDB instead.
   #
-  # = Advanced Fixtures
+  # == Advanced Fixtures
   #
   # Fixtures that don't specify an ID get some extra features:
   #
@@ -215,7 +225,7 @@ class FixtureClassNotFound < ActiveRecord::ActiveRecordError # :nodoc:
   # * Fixture label interpolation
   # * Support for YAML defaults
   #
-  # == Stable, Autogenerated IDs
+  # === Stable, Autogenerated IDs
   #
   # Here, have a monkey fixture:
   #
@@ -244,13 +254,13 @@ class FixtureClassNotFound < ActiveRecord::ActiveRecordError # :nodoc:
   # The generated ID for a given label is constant, so we can discover
   # any fixture's ID without loading anything, as long as we know the label.
   #
-  # == Label references for associations (+belongs_to+, +has_one+, +has_many+)
+  # === Label references for associations (+belongs_to+, +has_one+, +has_many+)
   #
   # Specifying foreign keys in fixtures can be very fragile, not to
   # mention difficult to read. Since Active Record can figure out the ID of
   # any fixture from its label, you can specify FK's by label instead of ID.
   #
-  # === +belongs_to+
+  # ==== +belongs_to+
   #
   # Let's break out some more monkeys and pirates.
   #
@@ -314,9 +324,9 @@ class FixtureClassNotFound < ActiveRecord::ActiveRecordError # :nodoc:
   #
   # Just provide the polymorphic target type and Active Record will take care of the rest.
   #
-  # === +has_and_belongs_to_many+ or <tt>has_many :through</tt>
+  # ==== +has_and_belongs_to_many+ or <tt>has_many :through</tt>
   #
-  # Time to give our monkey some fruit.
+  # \Time to give our monkey some fruit.
   #
   #   ### in monkeys.yml
   #
@@ -378,7 +388,7 @@ class FixtureClassNotFound < ActiveRecord::ActiveRecordError # :nodoc:
   # the fixture's model class and discovers the +has_and_belongs_to_many+
   # associations.
   #
-  # == Autofilled Timestamp Columns
+  # === Autofilled \Timestamp Columns
   #
   # If your table/model specifies any of Active Record's
   # standard timestamp columns (+created_at+, +created_on+, +updated_at+, +updated_on+),
@@ -386,7 +396,7 @@ class FixtureClassNotFound < ActiveRecord::ActiveRecordError # :nodoc:
   #
   # If you've set specific values, they'll be left alone.
   #
-  # == Fixture label interpolation
+  # === Fixture label interpolation
   #
   # The label of the current fixture is always available as a column value:
   #
@@ -407,7 +417,7 @@ class FixtureClassNotFound < ActiveRecord::ActiveRecordError # :nodoc:
   #
   #   ActiveRecord::FixtureSet.identify(:boaty_mcboatface, :uuid)
   #
-  # == Support for YAML defaults
+  # === Support for YAML defaults
   #
   # You can set and reuse defaults in your fixtures YAML file.
   # This is the same technique used in the +database.yml+ file to specify
@@ -583,7 +593,8 @@ def create_fixtures(fixtures_directories, fixture_set_names, class_names = {}, c
       end
 
       # Returns a consistent, platform-independent identifier for +label+.
-      # Integer identifiers are values less than 2^30. UUIDs are RFC 4122 version 5 SHA-1 hashes.
+      #
+      # \Integer identifiers are values less than 2^30. UUIDs are RFC 4122 version 5 SHA-1 hashes.
       def identify(label, column_type = :integer)
         if column_type == :uuid
           Digest::UUID.uuid_v5(Digest::UUID::OID_NAMESPACE, label.to_s)
@@ -596,7 +607,8 @@ def identify(label, column_type = :integer)
       # between the label and the subcomponents of the provided composite key.
       #
       # Example:
-      # composite_identify("label", [:a, :b, :c]) => { a: hash_1, b: hash_2, c: hash_3 }
+      #
+      #   composite_identify("label", [:a, :b, :c]) => { a: hash_1, b: hash_2, c: hash_3 }
       def composite_identify(label, key)
         key
           .index_with
@@ -604,7 +616,7 @@ def composite_identify(label, key)
           .with_indifferent_access
       end
 
-      # Superclass for the evaluation contexts used by ERB fixtures.
+      # Superclass for the evaluation contexts used by \ERB fixtures.
       def context_class
         @context_class ||= Class.new
       end
diff --git a/activerecord/lib/active_record/test_fixtures.rb b/activerecord/lib/active_record/test_fixtures.rb
index e4a5c4356f70d..8173d9e895d39 100644
--- a/activerecord/lib/active_record/test_fixtures.rb
+++ b/activerecord/lib/active_record/test_fixtures.rb
@@ -17,6 +17,16 @@ def after_teardown # :nodoc:
     end
 
     included do
+      ##
+      # :singleton-method: fixture_paths
+      #
+      # Returns the ActiveRecord::FixtureSet collection
+
+      ##
+      # :singleton-method: fixture_paths=
+      #
+      # :call-seq:
+      #   fixture_paths=(fixture_paths)
       class_attribute :fixture_paths, instance_writer: false, default: []
       class_attribute :fixture_table_names, default: []
       class_attribute :fixture_class_names, default: {}
@@ -42,7 +52,7 @@ def set_fixture_class(class_names = {})
         self.fixture_class_names = fixture_class_names.merge(class_names.stringify_keys)
       end
 
-      def fixture_path
+      def fixture_path # :nodoc:
         ActiveRecord.deprecator.warn(<<~WARNING)
           TestFixtures.fixture_path is deprecated and will be removed in Rails 7.2. Use .fixture_paths instead.
           If multiple fixture paths have been configured with .fixture_paths, then .fixture_path will just return
@@ -51,7 +61,7 @@ def fixture_path
         fixture_paths.first
       end
 
-      def fixture_path=(path)
+      def fixture_path=(path) # :nodoc:
         ActiveRecord.deprecator.warn("TestFixtures.fixture_path= is deprecated and will be removed in Rails 7.2. Use .fixture_paths= instead.")
         self.fixture_paths = Array(path)
       end
@@ -99,7 +109,7 @@ def uses_transaction?(method)
       end
     end
 
-    def fixture_path
+    def fixture_path # :nodoc:
       ActiveRecord.deprecator.warn(<<~WARNING)
         TestFixtures#fixture_path is deprecated and will be removed in Rails 7.2. Use #fixture_paths instead.
         If multiple fixture paths have been configured with #fixture_paths, then #fixture_path will just return
diff --git a/activesupport/lib/active_support/test_case.rb b/activesupport/lib/active_support/test_case.rb
index c28868bb0dd71..626d2087af1fa 100644
--- a/activesupport/lib/active_support/test_case.rb
+++ b/activesupport/lib/active_support/test_case.rb
@@ -120,6 +120,25 @@ def parallelize_setup(&block)
       def parallelize_teardown(&block)
         ActiveSupport::Testing::Parallelization.run_cleanup_hook(&block)
       end
+
+      # :singleton-method: fixture_paths
+      #
+      # Returns the ActiveRecord::FixtureSet collection.
+      #
+      # In your +test_helper.rb+ you must have <tt>require "rails/test_help"</tt>.
+
+      # :singleton-method: fixture_paths=
+      #
+      # :call-seq:
+      #   fixture_paths=(fixture_paths)
+      #
+      # Sets the given path to the fixture set.
+      #
+      # Can also append multiple paths.
+      #
+      #   ActiveSupport::TestCase.fixture_paths << "component1/test/fixtures"
+      #
+      # In your +test_helper.rb+ you must have <tt>require "rails/test_help"</tt>.
     end
 
     alias_method :method_name, :name