Why do I need to migrate the test database in Rails?

Question

After creating a new migration file, running the migration, then running my tests I receive:

Failure/Error: ActiveRecord::Migration.maintain_test_schema!

ActiveRecord::PendingMigrationError:

  Migrations are pending. To resolve this issue, run:

          bin/rails db:migrate RAILS_ENV=test

Isn't the following snippet in the rails_helper.rb supposed to apply the migrations to the test database for me?

# Checks for pending migration and applies them before tests are run.
# If you are not using ActiveRecord, you can remove this line.
ActiveRecord::Migration.maintain_test_schema!

Update

Here is my config/environments/test.rb as requested:

Rails.application.configure do
  # Settings specified here will take precedence over those in config/application.rb.

  # The test environment is used exclusively to run your application's
  # test suite. You never need to work with it otherwise. Remember that
  # your test database is "scratch space" for the test suite and is wiped
  # and recreated between test runs. Don't rely on the data there!
  config.cache_classes = true

  # Do not eager load code on boot. This avoids loading your whole application
  # just for the purpose of running a single test. If you are using a tool that
  # preloads Rails for running tests, you may have to set it to true.
  config.eager_load = false

  # Configure public file server for tests with Cache-Control for performance.
  config.public_file_server.enabled = true
  config.public_file_server.headers = {
    'Cache-Control' => 'public, max-age=3600'
  }

  # Show full error reports and disable caching.
  config.consider_all_requests_local       = true
  config.action_controller.perform_caching = false

  # Raise exceptions instead of rendering exception templates.
  config.action_dispatch.show_exceptions = false

  # Disable request forgery protection in test environment.
  config.action_controller.allow_forgery_protection = false
  config.action_mailer.perform_caching = false

  # Tell Action Mailer not to deliver emails to the real world.
  # The :test delivery method accumulates sent emails in the
  # ActionMailer::Base.deliveries array.
  config.action_mailer.delivery_method = :test

  # Print deprecation notices to the stderr.
  config.active_support.deprecation = :stderr

  # Raises error for missing translations
  # config.action_view.raise_on_missing_translations = true
end

Answer 1

On running your tests, the configurations are loaded in following order (unless you have customized the order of autoload_paths in your rails app):

1. config/application.rb
2. config/environments/test.rb
3. spec/rails_helper.rb

So, the migration pending error you are receiving must be due to config.active_record.migration_error = true this configuration setup somewhere before on the rails engine loads rails_helper.rb where ActiveRecord::Migration.maintain_test_schema! directive is defined.

Try setting config.active_record.migration_error = false on your config/environments/test.rb to skip migration check as it is described in rspec upgrade guide.