Share connection pools for non-default shards

Unless `legacy_connection_handling` was set to `false`, only the default
shard's connection pools were shared during transactional tests.

activerecord/lib/active_record/connection_adapters/legacy_pool_manager.rb

@@ -7,6 +7,10 @@ module ActiveRecord
         @name_to_pool_config = {}
       end
 
+      def shard_names
+        @name_to_pool_config.keys
+      end
+
       def pool_configs(_ = nil)
         @name_to_pool_config.values
       end

activerecord/lib/active_record/test_fixtures.rb

@@ -199,10 +199,11 @@ module ActiveRecord
                 writing_pool_manager = writing_handler.send(:owner_to_pool_manager)[name]
                 return unless writing_pool_manager
 
-                writing_pool_config = writing_pool_manager.get_pool_config(nil, :default)
-
                 pool_manager = handler.send(:owner_to_pool_manager)[name]
-                pool_manager.set_pool_config(nil, :default, writing_pool_config)
+                pool_manager.shard_names.each do |shard_name|
+                  writing_pool_config = writing_pool_manager.get_pool_config(nil, shard_name)
+                  pool_manager.set_pool_config(nil, shard_name, writing_pool_config)
+                end
               end
             end
           end

activerecord/test/cases/fixtures_test.rb

@@ -1447,8 +1447,22 @@ if current_adapter?(:SQLite3Adapter) && !in_memory_db?
     end
 
     def test_writing_and_reading_connections_are_the_same
-      rw_conn = ActiveRecord::Base.connection_handler.connection_pool_list(:writing).first.connection
-      ro_conn = ActiveRecord::Base.connection_handler.connection_pool_list(:reading).first.connection
+      handler = ActiveRecord::Base.connection_handler
+      rw_conn = handler.retrieve_connection_pool("ActiveRecord::Base", role: :writing).connection
+      ro_conn = handler.retrieve_connection_pool("ActiveRecord::Base", role: :reading).connection
+
+      assert_equal rw_conn, ro_conn
+    end
+
+    def test_writing_and_reading_connections_are_the_same_for_non_default_shards
+      ActiveRecord::Base.connects_to shards: {
+        default: { writing: :default, reading: :readonly },
+        two: { writing: :default, reading: :readonly }
+      }
+
+      handler = ActiveRecord::Base.connection_handler
+      rw_conn = handler.retrieve_connection_pool("ActiveRecord::Base", role: :writing, shard: :two).connection
+      ro_conn = handler.retrieve_connection_pool("ActiveRecord::Base", role: :reading, shard: :two).connection
 
       assert_equal rw_conn, ro_conn
     end
@@ -1525,8 +1539,23 @@ if current_adapter?(:SQLite3Adapter) && !in_memory_db?
       writing = ActiveRecord::Base.connection_handlers[:writing]
       reading = ActiveRecord::Base.connection_handlers[:reading]
 
-      rw_conn = writing.connection_pool_list.first.connection
-      ro_conn = reading.connection_pool_list.first.connection
+      rw_conn = writing.retrieve_connection_pool("ActiveRecord::Base").connection
+      ro_conn = reading.retrieve_connection_pool("ActiveRecord::Base").connection
+
+      assert_equal rw_conn, ro_conn
+    end
+
+    def test_writing_and_reading_connections_are_the_same_for_non_default_shards_with_legacy_handling
+      ActiveRecord::Base.connects_to shards: {
+        default: { writing: :default, reading: :readonly },
+        two: { writing: :default, reading: :readonly }
+      }
+
+      writing = ActiveRecord::Base.connection_handlers[:writing]
+      reading = ActiveRecord::Base.connection_handlers[:reading]
+
+      rw_conn = writing.retrieve_connection_pool("ActiveRecord::Base", shard: :two).connection
+      ro_conn = reading.retrieve_connection_pool("ActiveRecord::Base", shard: :two).connection
 
       assert_equal rw_conn, ro_conn
     end