Merge branch 'backstage/gb/improve-fast-specs-helper' into 'master'

Improve fast specs helper to autoload the library

See merge request gitlab-org/gitlab-ce!18903

doc/development/testing_guide/best_practices.md

@@ -133,11 +133,24 @@ really fast since:
 - gitlab-shell and Gitaly setup are skipped
 - Test repositories setup are skipped
 
-Note that in some cases, you might have to add some `require_dependency 'foo'`
-in your file under test since Rails autoloading is not available in these cases.
-
-This shouldn't be a problem since explicitely listing dependencies should be
-considered a good practice anyway.
+`fast_spec_helper` also support autoloading classes that are located inside the
+`lib/` directory. It means that as long as your class / module is using only
+code from the `lib/` directory you will not need to explicitly load any
+dependencies. `fast_spec_helper` also loads all ActiveSupport extensions,
+including core extensions that are commonly used in the Rails environment.
+
+Note that in some cases, you might still have to load some dependencies using
+`require_dependency` when a code is using gems or a dependency is not located
+in `lib/`.
+
+For example, if you want to test your code that is calling the
+`Gitlab::UntrustedRegexp` class, which under the hood uses `re2` library, you
+should either add `require_dependency 're2'` to files in your library that
+need `re2` gem, to make this requirement explicit, or you can add it to the
+spec itself, but the former is preferred.
+
+It takes around one second to load tests that are using `fast_spec_helper`
+instead of 30+ seconds in case of a regular `spec_helper`.
 
 ### `let` variables
 

spec/fast_spec_helper.rb

@@ -3,14 +3,8 @@ require 'bundler/setup'
 ENV['GITLAB_ENV'] = 'test'
 ENV['IN_MEMORY_APPLICATION_SETTINGS'] = 'true'
 
-unless Object.respond_to?(:require_dependency)
-  class Object
-    alias_method :require_dependency, :require
-  end
-end
-
-# Defines Settings and Gitlab.config which are at the center of the app
 require_relative '../config/settings'
-require_relative '../lib/gitlab' unless defined?(Gitlab.config)
-
 require_relative 'support/rspec'
+require 'active_support/all'
+
+ActiveSupport::Dependencies.autoload_paths << 'lib'