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Regression testing for data


 Project Readme


This gem provides a small DSL to check your data for inconsistencies and anomalies.

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Add this line to your application's Gemfile:

gem "data_checks"
$ bundle install
$ bin/rails generate data_checks:install


Making sure that data stays valid is not a trivial task. For simple requirements, like "this column is not null" or "this column is unique", you of course just use the database constraints and that's it. Same goes for type validation or reference integrity.

However, when you want to check for something more complex, then it all changes. Depending on your DBMS, you can use stored procedures, but this is often harder to write, version and maintain.

You could also assume that your data will never get corrupted, and validations directly in the code can do the trick ... but that'd be way too optimistic. Bugs happen all the time, and it's best to plan for the worst.

This gem doesn't aim to replace those tools, but provides something else that could serve a close purpose: ensure that you work with the data you expect.

This gem helps you to schedule some verifications on your data and get alerts when something is unexpected.

data_checks can help to catch:

  • 🐛 Bugs due to race conditions (e.g. user accidentally double clicks a button to delete an email and ends up without emails due to a race condition bug in the app)
  • 🐛 Invalid persisted data
  • 🐛 Unexpected changes in behavior and data (e.g. too many (too less) of something is created/deleted/imported/enqueued/..., etc)

This idea is nicely presented at RailsConf: RailsConf 2018: The Doctor Is In: Using checkups to find bugs in production by Ryan Laughlin


A small DSL is provided to help express predicates and an easy way to configure notifications.

You will be notified when a check starts failing, and when it starts passing again.

Checking for inconsistencies

For example, we expect every image attachment to have previews in 3 sizes. It is possible, that when a new image was attached, some previews were not generated because of some failure. What we would like to ensure is that no image ends up without a full set of previews. We could write something like:

DataChecks.configure do
  ensure_no :users_without_emails, tag: "minutely" do

  ensure_no :images_without_previews, tag: "hourly" do
      .having("COUNT(previews.id) < 3")

  notifier :email,
    from: "production@company.com",
    to: "developer@company.com"

Checking for anomalies

This gem can be also used to detect anomalies in the data. For example, you expect to have some number of new orders in the system in some period of time. Otherwise, this can hint at some bug in the order placing system worth investigating.

ensure_more :new_orders_per_hour, than: 10, tag: "hourly" do
  Order.where("created_at >= ?", 1.hour.ago).count


Custom configurations should be placed in a data_checks.rb initializer.

# config/initializers/data_checks.rb

DataChecks.configure do
  # ...


Currently, the following notifiers are supported:

  • :email: Uses ActionMailer to send emails. You can pass it any ActionMailer options.
  • :slack: Sends notifications to Slack. Accepts the following options:
    • webhook_url: The webhook url to send notifications to
  • :logger: Uses Logger to output notifications to the log. Accepts the following params:
    • logdev: The log device. This is a filename (String) or IO object (typically STDOUT, STDERR, or an open file).
    • level: Logging severity threshold (e.g. Logger::INFO)

Each of them accepts a formatter_class config to configure the used formatter when generating a notification.

You can create custom notifiers by creating a subclass of Notifier.

Create a notifier:

notifier :email,
  from: "production@company.com",
  to: "developer@company.com"

Create multiple notifiers of the same type:

notifier "developers",
  type: :email,
  from: "production@company.com",
  to: ["developer1@company.com", "developer2@company.com"]

notifier "tester",
  type: :email,
  from: "production@company.com",
  to: "tester@company.com"

ensure_no :images_without_previews, notify: "developers" do # notify only developers
  # ...


  • ensure_no will check that the result of a given block is zero?, empty? or false
  • ensure_any will check that the result of a given block is > 0
  • ensure_more will check that the result of a given block is > than a given number or that it contains more than a given number of items
  • ensure_less will check that the result of a given block is < than a given number or that it contains less than a given number of items
  • ensure_equal will check that the result of a given block is == to the given number or that it contains a given number of items
ensure_no :images_without_previews do
  # ...

ensure_any :facebook_logins_per_hour do
  # ...

ensure_more :new_orders_per_hour, than: 10 do
  # ...

Customizing the error handler

Exceptions raised while a check runs are rescued and information about the error is persisted in the database.

If you want to integrate with an exception monitoring service (e.g. Bugsnag), you can define an error handler:

# config/initializers/data_checks.rb

DataChecks.config.error_handler = ->(error, check_context) do
  Bugsnag.notify(error) do |notification|
    notification.add_metadata(:data_checks, check_context)

The error handler should be a lambda that accepts 2 arguments:

  • error: The exception that was raised.
  • check_context: A hash with additional information about the check:
    • check_name: The name of the check that errored
    • ran_at: The time when the check ran

Customizing the backtrace cleaner

DataChecks.config.backtrace_cleaner can be configured to specify a backtrace cleaner to use when a check errors and the backtrace is cleaned and persisted. An ActiveSupport::BacktraceCleaner should be used.

# config/initializers/data_checks.rb

cleaner = ActiveSupport::BacktraceCleaner.new
cleaner.add_silencer { |line| line =~ /ignore_this_dir/ }

DataChecks.config.backtrace_cleaner = cleaner

If none is specified, the default Rails.backtrace_cleaner will be used to clean backtraces.

Schedule checks

Schedule checks to run (with cron, Heroku Scheduler, etc).

rake data_checks:run_checks TAG="5 minutes"  # run checks with tag="5 minutes"
rake data_checks:run_checks TAG="hourly"     # run checks with tag="hourly"
rake data_checks:run_checks TAG="daily"      # run checks with tag="daily"
rake data_checks:run_checks                  # run all checks

Here's what it looks like with cron.

*/5 * * * * rake data_checks:run_checks TAG="5 minutes"
0   * * * * rake data_checks:run_checks TAG="hourly"
30  7 * * * rake data_checks:run_checks TAG="daily"

You can also manually get a status of all the checks by running:

rake data_checks:status


Thanks to checker_jobs gem for the original idea.


After checking out the repo, run bundle install to install dependencies. Then, run rake test to run the tests.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.


Bug reports and pull requests are welcome on GitHub at https://github.com/fatkodima/data_checks.


The gem is available as open source under the terms of the MIT License.