switching between truncation and transaction clean-up

[akostadinov]

#2579 switched from default truncation clean-up to default transaction clean-up. Switching between the two only worked for @javascript tagged scenarios instead of the intended list of scenario tags. It turned out to be a problem for postgres database and Groups and permissions cucumber feature.

This PR removes special @javascript tag handling by cucumber-rails (by implementing a null strategy) and uses simple DatabaseCleaner strategy switching in Before hooks.

For more information about @javscript handling see documentation at [1], in-built hooks [2] and the strategies these hooks apply to [3]. Also a discussion describing the different kinds of problems cucumber/cucumber-rails#166.

[1] https://github.com/cucumber/cucumber-rails/blob/561ee249c418f1c8cd7b629e7cf414442ce62709/features/choose_javascript_database_strategy.feature
[2] https://github.com/cucumber/cucumber-rails/blob/561ee249c418f1c8cd7b629e7cf414442ce62709/lib/cucumber/rails/hooks/active_record.rb
[3] https://github.com/cucumber/cucumber-rails/tree/0b2a8fddc74dff6f773468b919ed9f625685db2a/lib/cucumber/rails/database
[4] cucumber/cucumber-rails#166

[hallelujah]

This should not be needed. It was not before upgrade to Cucumber 7. Also it is not needed for MySQL

I think the issue lies on some DB feature.

[akostadinov]

@hallelujah , before #2579 test ran in truncation mode. If you check references in description, especially cucumber/cucumber-rails#166 people report that drivers are not thread safe and strange effects may appear.

This PR makes switching between truncation and transaction mode work. Before it, only @javascript tagged scenarios ran in truncation mode.

I don't know what kind of database feature may affect this scenario. Please provide any suggestions. It might be something specific about how Postgresql driver works because some people reported one thread doing a query and another thread receiving the result.

[hallelujah]

The Cucumber::Rails::Database is supposed to abstract the underlying DatabaseCleaner

I think we should not expose DatabaseCleaner here

[akostadinov]

It does not. Cucumber::Rails::Database.javascript_strategy only affects @javascript tagged scenarios and nothing else.

See https://github.com/cucumber/cucumber-rails/blob/561ee249c418f1c8cd7b629e7cf414442ce62709/lib/cucumber/rails/hooks/active_record.rb

I have another commit that allows switching between truncation, transaction with threading hack and transaction without threading hack but it is needlessly complicated and we don't need it. See 2a16ffbeab79b9258a200b3d6dd8621e3223b7f7. Also see my cucumber/cucumber-rails#521 where I discuss this with upstream project.

[hallelujah]

I do not understand why we had to separate the concerns.

The cucumber database strategy should call before_js and such ... Those methods then set/unset the DatabaseCleaner strategy. Now you are separating concerns which is confusing.
I think the issue is the order of when those methods are called (as they are callbacks)

# I think this should be enough:

Before non_transactional do
  Cucumber::Rails::Database.javascript_strategy = :truncation
end

But the callbacks should be called like this:

• Cucumber::Rails::Database.javascript_strategy = :truncation
• Cucumber::Rails::Database.strategy.before_js
• run your tests
• Cucumber::Rails::Database.strategy.after

My guess is that the order of the call of the callbacks is wrong

The issue is probably before_js (of transaction strategy) is called before setting the javascript_strategy = :truncation ... which makes it enter a transaction then truncate which will autocommit as it is a DDL statement

This is what I debugged for MySQL. And I am deeply sorry I did not dig deeper for other DBs (really my fault) as I was supposing it was the same for other DB

Probably there is something either in the code or in the cucumber-* or rails-* or oracle-* gems that creates this issue for Postgres and Oracle

[akostadinov]

In-built hooks run after our defined hooks and mess-up everything. They only regard @javascript and not @javascript so our tag lists become irrelevant.

[hallelujah]