Fixed automatic maintaining test schema to properly handle sql structure schema format.

Additionally:
* It changes `purge` task on `sqlite3` adapter to recreate database file, to
be consistent with other adapters.
* Adds `purge` step when loading from `schema.rb`

activerecord/CHANGELOG.md

+*   Fixed automatic maintaining test schema to properly handle sql structure
+    schema format. Fixes #15394.
+
+    *Wojciech Wnętrzak*
+
 *   PostgreSQL support default values for enum types. Fixes #7814.
 
     *Yves Senn*

activerecord/lib/active_record/tasks/database_tasks.rb

@@ -161,10 +161,12 @@ def load_schema(format = ActiveRecord::Base.schema_format, file = nil)
         when :ruby
           file ||= File.join(db_dir, "schema.rb")
           check_schema_file(file)
+          purge(current_config)
           load(file)
         when :sql
           file ||= File.join(db_dir, "structure.sql")
           check_schema_file(file)
+          purge(current_config)
           structure_load(current_config, file)
         else
           raise ArgumentError, "unknown format #{format.inspect}"

activerecord/lib/active_record/tasks/sqlite_database_tasks.rb

@@ -21,7 +21,11 @@ def drop
 
         FileUtils.rm(file) if File.exist?(file)
       end
-      alias :purge :drop
+
+      def purge
+        drop
+        create
+      end
 
       def charset
         connection.encoding

railties/test/application/test_test.rb

@@ -125,12 +125,12 @@ class UserTest < ActiveSupport::TestCase
 
       assert_unsuccessful_run "models/user_test.rb", "Migrations are pending"
 
-      app_file 'db/structure.sql', <<-RUBY
+      app_file 'db/structure.sql', <<-SQL
         CREATE TABLE "schema_migrations" ("version" varchar(255) NOT NULL);
         CREATE UNIQUE INDEX "unique_schema_migrations" ON "schema_migrations" ("version");
         CREATE TABLE "users" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "name" varchar(255));
         INSERT INTO schema_migrations (version) VALUES ('#{version}');
-      RUBY
+      SQL
 
       app_file 'config/initializers/disable_maintain_test_schema.rb', <<-RUBY
         Rails.application.config.active_record.maintain_test_schema = false
@@ -143,6 +143,56 @@ class UserTest < ActiveSupport::TestCase
       assert_successful_test_run('models/user_test.rb')
     end
 
+    test "sql structure migrations when adding column to existing table" do
+      output_1  = script('generate model user name:string')
+      version_1 = output_1.match(/(\d+)_create_users\.rb/)[1]
+
+      app_file 'test/models/user_test.rb', <<-RUBY
+        require 'test_helper'
+        class UserTest < ActiveSupport::TestCase
+          test "user" do
+            User.create! name: "Jon"
+          end
+        end
+      RUBY
+
+      app_file 'config/initializers/enable_sql_schema_format.rb', <<-RUBY
+        Rails.application.config.active_record.schema_format = :sql
+      RUBY
+
+      app_file 'db/structure.sql', <<-SQL
+        CREATE TABLE "schema_migrations" ("version" varchar(255) NOT NULL);
+        CREATE UNIQUE INDEX "unique_schema_migrations" ON "schema_migrations" ("version");
+        CREATE TABLE "users" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "name" varchar(255));
+        INSERT INTO schema_migrations (version) VALUES ('#{version_1}');
+      SQL
+
+      assert_successful_test_run('models/user_test.rb')
+
+      output_2  = script('generate migration add_email_to_users')
+      version_2 = output_2.match(/(\d+)_add_email_to_users\.rb/)[1]
+
+      app_file 'test/models/user_test.rb', <<-RUBY
+        require 'test_helper'
+
+        class UserTest < ActiveSupport::TestCase
+          test "user" do
+            User.create! name: "Jon", email: "jon@doe.com"
+          end
+        end
+      RUBY
+
+      app_file 'db/structure.sql', <<-SQL
+        CREATE TABLE "schema_migrations" ("version" varchar(255) NOT NULL);
+        CREATE UNIQUE INDEX "unique_schema_migrations" ON "schema_migrations" ("version");
+        CREATE TABLE "users" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "name" varchar(255), "email" varchar(255));
+        INSERT INTO schema_migrations (version) VALUES ('#{version_1}');
+        INSERT INTO schema_migrations (version) VALUES ('#{version_2}');
+      SQL
+
+      assert_successful_test_run('models/user_test.rb')
+    end
+
     private
       def assert_unsuccessful_run(name, message)
         result = run_test_file(name)