use foreign key DSL in our tests.

activerecord/test/cases/adapters/mysql2/schema_migrations_test.rb

@@ -6,12 +6,12 @@ class Mysql2Adapter
       class SchemaMigrationsTest < ActiveRecord::TestCase
         def test_renaming_index_on_foreign_key
           connection.add_index "engines", "car_id"
-          connection.execute "ALTER TABLE engines ADD CONSTRAINT fk_engines_cars FOREIGN KEY (car_id) REFERENCES cars(id)"
+          connection.add_foreign_key :engines, :cars, name: "fk_engines_cars"
 
           connection.rename_index("engines", "index_engines_on_car_id", "idx_renamed")
           assert_equal ["idx_renamed"], connection.indexes("engines").map(&:name)
         ensure
-          connection.execute "ALTER TABLE engines DROP FOREIGN KEY fk_engines_cars"
+          connection.remove_foreign_key :engines, name: "fk_engines_cars"
         end
 
         def test_initializes_schema_migrations_for_encoding_utf8mb4

activerecord/test/schema/schema.rb

@@ -860,9 +860,8 @@ def except(adapter_names_to_exclude)
     create_table :fk_test_has_pk, force: true, primary_key: "pk_id" do |t|
     end
 
-    execute "ALTER TABLE fk_test_has_fk ADD CONSTRAINT fk_name FOREIGN KEY (#{quote_column_name 'fk_id'}) REFERENCES #{quote_table_name 'fk_test_has_pk'} (#{quote_column_name 'pk_id'})"
-
-    execute "ALTER TABLE lessons_students ADD CONSTRAINT student_id_fk FOREIGN KEY (#{quote_column_name 'student_id'}) REFERENCES #{quote_table_name 'students'} (#{quote_column_name 'id'})"
+    add_foreign_key :fk_test_has_fk, :fk_test_has_pk, column: "fk_id", name: "fk_name", primary_key: "pk_id"
+    add_foreign_key :lessons_students, :students
   end
 
   create_table :overloaded_types, force: true do |t|