Add tests for `JobIteration::TestHelper` #1573

Job	Run time
Lint	8s
Ruby 2.6 \| Rails 5.2 \| Gemfile rails_gems	1m 3s
Ruby 2.6 \| Rails 6.0 \| Gemfile rails_gems	1m 3s
Ruby 2.6 \| Rails 6.1 \| Gemfile rails_gems	1m 0s
Ruby 2.7 \| Rails 5.2 \| Gemfile rails_gems	49s
Ruby 2.7 \| Rails 6.0 \| Gemfile rails_gems	57s
Ruby 2.7 \| Rails 6.1 \| Gemfile rails_gems	50s
Ruby 2.7 \| Rails 7.0 \| Gemfile rails_gems	53s
Ruby 3.0 \| Rails 6.0 \| Gemfile rails_gems	43s
Ruby 3.0 \| Rails 6.1 \| Gemfile rails_gems	39s
Ruby 3.0 \| Rails 7.0 \| Gemfile rails_gems	40s
Ruby 3.1 \| Rails 6.1 \| Gemfile rails_gems	46s
Ruby 3.1 \| Rails 7.0 \| Gemfile rails_gems	51s
Ruby 3.1 \| Rails 7.1 \| Gemfile rails_gems	54s
Ruby 3.1 \| Rails edge \| Gemfile rails_gems	52s
Ruby 3.2 \| Rails 7.0 \| Gemfile rails_gems	48s
Ruby 3.2 \| Rails 7.1 \| Gemfile rails_gems	46s
Ruby 3.2 \| Rails edge \| Gemfile rails_gems	37s
Ruby 3.3 \| Rails 7.0 \| Gemfile rails_gems	42s
Ruby 3.3 \| Rails 7.1 \| Gemfile rails_gems	36s
Ruby 3.3 \| Rails edge \| Gemfile rails_gems	52s
Ruby head \| Rails edge \| Gemfile rails_gems	48s
	17m 17s

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