Mocha::StateMachine states method stomps on states fixture

[DBugger32]

Attempting to upgrade to Rails 7.1.1, and running into a namespace issue. It appears the Mocha::StateMachine collection is hijacking the states fixture.

Ruby version is 3.2.2.

After upgrading from Rails 7.0.8 to 7.1.1, I am getting this error running a test that uses the fixture named states...

NoMethodError: undefined method display_name' for #<Mocha::StateMachine:0x0000000143434470 @name=:robonia, @current_state=nil>`

Have a simple active record class called State, that references the states table.

There are a few fixture records we use for testing.

And a test class that exists basically to test one method of the State class

require 'test_helper'

class StateTest < ActiveSupport::TestCase
   fixtures :states
   it 'returns #abbreviation - #name' do
      assert_equal 'RB - Robonia', states(:robonia).display_name
   end
end

Here is the top of the TestHelper class...

ENV['RAILS_ENV'] ||= 'test'
require_relative "../config/environment"
require 'rails/test_help'
require 'minitest/autorun'
require 'mocha/minitest'

Realize while typing this, that it might be a class loader issue of some sort.

[James Mead]

Hmm. Mocha has implemented the Mocha::API#states method for many years, so something must've changed in Rails. I'm not very familiar with fixtures these days, but it looks as if Rails must be magically defining a #states method and somehow making that available from within the tests. I'm guessing that in Rails v7.0.8 this was happening after require 'mocha/minitest', but in Rails v7.1.1 it's happening before this point.

Looking into it a bit more, this Rails PR which was included in Rails v7.1.0.beta1 looks very suspicious. It looks like it's changed from defining the fixture accessor methods up-front to relying on a method_missing implementation and presumably Mocha::API#states is intercepting the relevant calls.

I can't immediate think of a nice way around this. Perhaps you could rename the fixture accessor somehow, e.g. rename the YML file to e.g. my_states.yml and either use model_class within the YML or ActiveRecord::TestFixtures::ClassMethods#set_fixture_class in the test to specify the model class as State...?

[James Mead]

Another option might be to define another #states method in the relevant test to "override" Mocha::API#states and then call the fixture accessor via #method_missing, e.g.

require 'test_helper'

class StateTest < ActiveSupport::TestCase
  fixtures :states
  it 'returns #abbreviation - #name' do
    assert_equal 'RB - Robonia', states(:robonia).display_name
  end

  private
  def states
    method_missing(:states)
  end
end

I haven't actually tried this so YMMV!

[DBugger32]

Thank you for the quick response and from saving me to having to dig into the Rails source. Will try the suggested workarounds. Will close the issue -- because this clearly not a mocha problem.

[James Mead]

Thank you for the quick response and from saving me to having to dig into the Rails source.

No worries - I hope that was the relevant change!

Will try the suggested workarounds.

Good luck! 🤞 Let me know if they work!

Will close the issue -- because this clearly not a mocha problem.

Thanks. I think one could argue that Mocha shouldn't add a method with such a common name to the test context, but given this is the first time I've heard about this being a problem, I'm not planning to make a change at this stage.

[DBugger32]

Confess, I simply stopped using the :states fixture in the first repo. But, while bumping another app where the State class has some more meat, I had to actually implement a workaround.

1. renamed states.yml -> us_states.yml
2. added set_fixture_class(us_states: State) to class ActiveSupport::TestCase
3. renamed all references to the :states fixture to :us_states

let(:ct) { us_states(:CT) }

And we're green again.

[James Mead]

@DBugger32 Cool! Thanks for letting me know! 👍