Rake test fails with 'uninitialized constant ApplicationHelper (NameError)' after migration from Rails 6.1 to 7.0

After upgrade our app from Rails 6.1 to Rails 7.0, ‘rake test’ fails to run: .rvm/gems/ruby-3.0.6/gems/activesupport-7.0.8.1/lib/active_support/inflector/methods.rb:278:in `constantize’: uninitialized constant ApplicationHelper (NameError)

That file is in app/helpers.