Add test case for deprecated `insert_fixtures`

Since #31422, `insert_fixtures` is deprecated.

activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb

@@ -367,9 +367,11 @@ def foreign_keys(table_name)
       end
 
       def insert_fixtures(rows, table_name)
-        rows.each do |row|
-          insert_fixture(row, table_name)
-        end
+        ActiveSupport::Deprecation.warn(<<-MSG.squish)
+          `insert_fixtures` is deprecated and will be removed in the next version of Rails.
+          Consider using `insert_fixtures_set` for performance improvement.
+        MSG
+        insert_fixtures_set(table_name => rows)
       end
 
       def insert_fixtures_set(fixture_set, tables_to_delete = [])

activerecord/test/cases/fixtures_test.rb

@@ -211,16 +211,30 @@ def test_no_auto_value_on_zero_is_disabled
       subscription = ActiveSupport::Notifications.subscribe("sql.active_record", subscriber)
 
       assert_nothing_raised do
-        ActiveRecord::Base.connection.insert_fixtures(fixtures, "aircraft")
+        ActiveRecord::Base.connection.insert_fixtures_set("aircraft" => fixtures)
       end
 
-      expected_sql = "INSERT INTO `aircraft` (`id`, `name`, `wheels_count`) VALUES (DEFAULT, 'first', 2), (DEFAULT, 'second', 3)"
+      expected_sql = "INSERT INTO `aircraft` (`id`, `name`, `wheels_count`) VALUES (DEFAULT, 'first', 2), (DEFAULT, 'second', 3);\n"
       assert_equal expected_sql, subscriber.events.first
     ensure
       ActiveSupport::Notifications.unsubscribe(subscription)
     end
   end
 
+  def test_deprecated_insert_fixtures
+    fixtures = [
+      { "name" => "first", "wheels_count" => 2 },
+      { "name" => "second", "wheels_count" => 3 }
+    ]
+    conn = ActiveRecord::Base.connection
+    conn.delete("DELETE FROM aircraft")
+    assert_deprecated do
+      conn.insert_fixtures(fixtures, "aircraft")
+    end
+    result = conn.select_all("SELECT name, wheels_count FROM aircraft ORDER BY id")
+    assert_equal fixtures, result.to_a
+  end
+
   def test_broken_yaml_exception
     badyaml = Tempfile.new ["foo", ".yml"]
     badyaml.write "a: : "