How to fix ActiveRecord::DangerousAttributeError when checking pending migration in RSpec spec_helper?

Question

Okay so this is a new one. RSPec. Rails 4.

This line is in my spec_helper.rb:

# Checks for pending migrations before tests are run.
# If you are not using ActiveRecord, you can remove this line.
ActiveRecord::Migration.check_pending! if defined?(ActiveRecord::Migration)

When I run a simple test (on an ActiveRecord model):

it { should respond_to :activity }

I get the following error & trace:

/Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord 4.0.0/lib/active_record/attribute_methods.rb:59:in `instance_method_already_implemented?': version is defined by Active Record (ActiveRecord::DangerousAttributeError)
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activemodel-4.0.0/lib/active_model/attribute_methods.rb:282:in `block in define_attribute_method'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activemodel-4.0.0/lib/active_model/attribute_methods.rb:279:in `each'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activemodel-4.0.0/lib/active_model/attribute_methods.rb:279:in `define_attribute_method'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activemodel-4.0.0/lib/active_model/attribute_methods.rb:246:in `block in define_attribute_methods'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activemodel-4.0.0/lib/active_model/attribute_methods.rb:246:in `each'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activemodel-4.0.0/lib/active_model/attribute_methods.rb:246:in `define_attribute_methods'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/attribute_methods.rb:29:in `block in define_attribute_methods'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/attribute_methods.rb:26:in `synchronize'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/attribute_methods.rb:26:in `define_attribute_methods'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/attribute_methods.rb:167:in `respond_to?'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activesupport-4.0.0/lib/active_support/callbacks.rb:368:in `__define_callbacks'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activesupport-4.0.0/lib/active_support/callbacks.rb:79:in `run_callbacks'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/core.rb:216:in `init_with'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/persistence.rb:55:in `instantiate'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/querying.rb:45:in `block in find_by_sql'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/result.rb:21:in `block in each'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/result.rb:21:in `each'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/result.rb:21:in `each'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/querying.rb:45:in `map'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/querying.rb:45:in `find_by_sql'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/relation.rb:585:in `exec_queries'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/relation.rb:471:in `load'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/relation.rb:220:in `to_a'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/relation/delegation.rb:12:in `map'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/migration.rb:787:in `get_all_versions'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/migration.rb:793:in `current_version'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/migration.rb:800:in `needs_migration?'
    from /Users/dev/.rvm/gems/ruby-2.0.0-p247@projectname/gems/activerecord-4.0.0/lib/active_record/migration.rb:379:in `check_pending!'
    from /projects/subset_of_projects/this_project_group/projectname/spec/spec_helper.rb:17:in `<top (required)>'

Answer 1

I'd added the paper_trail gem but not run the install/migrations. Simple and obvious really. But it wasn't an error I'd seen before so I'll post this so others who might run into it can check the obvious before wasting a long time on this.