bring back `db:test:prepare`.

This reverts deprecations added in #13528.
The task is brought back for two reasons:
  1. Give plugins a way to hook into the test database initialization process
  2. Give the user a way to force a test database synchronization

While `test:prepare` is still a dependency of every test task, `db:test:prepare`
no longer hooks into it. This means that `test:prepare` runs before the schema
is synchronized. Plugins, which insert data can now hook into `db:test:prepare`.

The automatic schema maintenance can't detect when a migration is rolled-back,
modified and reapplied. In this case the user has to fall back to `db:test:prepare`
to force the synchronization to happen.

2 files changed, 92 insertions, 9 deletions

diff --git a/railties/test/application/rake/dbs_test.rb b/railties/test/application/rake/dbs_test.rb
index 524c70aad2..0a5873bcbf 100644
--- a/railties/test/application/rake/dbs_test.rb
+++ b/railties/test/application/rake/dbs_test.rb
@@ -175,15 +175,6 @@ module ApplicationTests
         db_test_load_structure
       end
 
-      test 'db:test deprecation' do
-        require "#{app_path}/config/environment"
-        Dir.chdir(app_path) do
-          output = `bundle exec rake db:migrate db:test:prepare 2>&1`
-          assert_equal "WARNING: db:test:prepare is deprecated. The Rails test helper now maintains " \
-                       "your test schema automatically, see the release notes for details.\n", output
-        end
-      end
-
       test 'db:setup loads schema and seeds database' do
         begin
           @old_rails_env = ENV["RAILS_ENV"]
diff --git a/railties/test/application/test_test.rb b/railties/test/application/test_test.rb
index 4d06056280..c7132837b1 100644
--- a/railties/test/application/test_test.rb
+++ b/railties/test/application/test_test.rb
@@ -193,6 +193,98 @@ module ApplicationTests
       assert_successful_test_run('models/user_test.rb')
     end
 
+    # TODO: would be nice if we could detect the schema change automatically.
+    # For now, the user has to synchronize the schema manually.
+    # This test-case serves as a reminder for this use-case.
+    test "manually synchronize test schema after rollback" do
+      output  = script('generate model user name:string')
+      version = output.match(/(\d+)_create_users\.rb/)[1]
+
+      app_file 'test/models/user_test.rb', <<-RUBY
+        require 'test_helper'
+
+        class UserTest < ActiveSupport::TestCase
+          test "user" do
+            assert_equal ["id", "name"], User.columns_hash.keys
+          end
+        end
+      RUBY
+      app_file 'db/schema.rb', <<-RUBY
+        ActiveRecord::Schema.define(version: #{version}) do
+          create_table :users do |t|
+            t.string :name
+          end
+        end
+      RUBY
+
+      assert_successful_test_run "models/user_test.rb"
+
+      # Simulate `db:rollback` + edit of the migration file + `db:migrate`
+      app_file 'db/schema.rb', <<-RUBY
+        ActiveRecord::Schema.define(version: #{version}) do
+          create_table :users do |t|
+            t.string :name
+            t.integer :age
+          end
+        end
+      RUBY
+
+      assert_successful_test_run "models/user_test.rb"
+
+      Dir.chdir(app_path) { `bin/rake db:test:prepare` }
+
+      assert_unsuccessful_run "models/user_test.rb", <<-ASSERTION
+Expected: ["id", "name"]
+  Actual: ["id", "name", "age"]
+      ASSERTION
+    end
+
+    test "hooks for plugins" do
+      output  = script('generate model user name:string')
+      version = output.match(/(\d+)_create_users\.rb/)[1]
+
+      app_file 'lib/tasks/hooks.rake', <<-RUBY
+        task :before_hook do
+          has_user_table = ActiveRecord::Base.connection.table_exists?('users')
+          puts "before: " + has_user_table.to_s
+        end
+
+        task :after_hook do
+          has_user_table = ActiveRecord::Base.connection.table_exists?('users')
+          puts "after: " + has_user_table.to_s
+        end
+
+        Rake::Task["db:test:prepare"].enhance [:before_hook] do
+          Rake::Task[:after_hook].invoke
+        end
+      RUBY
+      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
+
+      # Simulate `db:migrate`
+      app_file 'db/schema.rb', <<-RUBY
+        ActiveRecord::Schema.define(version: #{version}) do
+          create_table :users do |t|
+            t.string :name
+          end
+        end
+      RUBY
+
+      output = assert_successful_test_run "models/user_test.rb"
+      assert_includes output, "before: false\nafter: true"
+
+      # running tests again won't trigger a schema update
+      output = assert_successful_test_run "models/user_test.rb"
+      assert_not_includes output, "before:"
+      assert_not_includes output, "after:"
+    end
+
     private
       def assert_unsuccessful_run(name, message)
         result = run_test_file(name)