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.

Answer 2

It might be because of two reasons.

1. You may have missed it to configure in config/environments/test.rb

Add config.active_record.maintain_test_schema = true if you don't have it or set it to true if you had set it to false.

From the docs

config.active_record.maintain_test_schema is a boolean value which controls whether Active Record should try to keep your test database schema up-to-date with db/schema.rb (or db/structure.sql) when you run your tests. The default is true.

2. You might have pending migrations after the schema has loaded

From the rspec docs

What this does is that rather than just raising when the test schema has pending migrations, Rails will try to load the schema. An exception will now only be raised if there are pending migrations afterwards the schema has been loaded.

Check whether you have pending migrations with rake db:migrate:status

Also, If you are using SQLite 3.7.9, you should take a look at this discussion

Answer 3

You should run rails db:migrate RAILS_ENV=test to update your test DB first.

What this does is that, rather than just raising when the test schema has pending migrations, Rails will try to load the schema. An exception will now only be raised if there are pending migrations afterwards the schema has been loaded.

There are a few caveats to be aware of when using this:

• Migrations still need to be run manually; although now this only has to be done in the 'development' environment.
• An exception will be raised if the schema has not been initialized. The exception will provide instructions stating rake db:migrate needs to be run.