Loading fixture in a before :context raise an exception

[mdesantis]

Loading fixture in a before :context raise an exception:

NoMethodError:
  undefined method `[]' for nil:NilClass
# /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/activerecord-4.1.6/lib/active_record/fixtures.rb:897:in `block (3 levels) in setup_fixture_accessors'

I created a Rails app in order to reproduce it: https://github.com/mdesantis/rspec-rails-issue-1201.

Environment: Ruby 2.1.3, Rails 4.1.6, rspec-rails 3.1.0

Failing test: (spec/models/widget_spec.rb):

require 'rails_helper'

RSpec.describe Widget, type: :model do
  fixtures :widgets

  describe 'fixture loaded in a before context' do
    before :context do
      widgets :a
    end

    it 'works' do
    end
  end
end

This is the specs run output:

$ rspec -b
F

Failures:

  1) Widget fixture loaded in a before context works
     Failure/Error: widgets :a
     NoMethodError:
       undefined method `[]' for nil:NilClass
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/activerecord-4.1.6/lib/active_record/fixtures.rb:897:in `block (3 levels) in setup_fixture_accessors'
     # ./spec/models/widget_spec.rb:8:in `block (3 levels) in <top (required)>'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/hooks.rb:350:in `instance_exec'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/hooks.rb:350:in `run'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/hooks.rb:459:in `run'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/hooks.rb:500:in `run'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example_group.rb:426:in `block in run_before_context_hooks'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/memoized_helpers.rb:141:in `block in isolate_for_context_hook'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/memoized_helpers.rb:137:in `instance_exec'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/memoized_helpers.rb:137:in `isolate_for_context_hook'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example_group.rb:425:in `run_before_context_hooks'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example_group.rb:452:in `run'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example_group.rb:454:in `block in run'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example_group.rb:454:in `map'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/example_group.rb:454:in `run'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:111:in `block (2 levels) in run_specs'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:111:in `map'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:111:in `block in run_specs'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/reporter.rb:53:in `report'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:107:in `run_specs'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:85:in `run'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:69:in `run'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/lib/rspec/core/runner.rb:37:in `invoke'
     # /home/mdesantis/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/rspec-core-3.1.7/exe/rspec:4:in `<top (required)>'
     # /home/mdesantis/.rbenv/versions/2.1.3/bin/rspec:23:in `load'
     # /home/mdesantis/.rbenv/versions/2.1.3/bin/rspec:23:in `<main>'
     # /home/mdesantis/.rbenv/versions/2.1.3/bin/ruby_executable_hooks:15:in `eval'
     # /home/mdesantis/.rbenv/versions/2.1.3/bin/ruby_executable_hooks:15:in `<main>'

Finished in 0.0012 seconds (files took 3.14 seconds to load)
1 example, 1 failure

Failed examples:

rspec ./spec/models/widget_spec.rb:11 # Widget fixture loaded in a before context works

[cupakromer]

💙 Thanks for the repo repo 😺 @mdesantis! That really helps us out a lot.

Why not use before(:example)? What is your need for a before(:context) in this case?

I just wanted to get my main question at the top of this reply instead of burying at the end. Now to elaborate further, this is expected behavior. When you send the fixtures message to the RSpec context it will load those fixture helper methods for an example. The before(:context) occurs before the transactional example scope. The reason for this is that the transactional mechanism is not setup yet. We have this hidden in the docs here:

Data created in before(:all) are not rolled back

before(:all) hooks are invoked before the transaction is opened. You can use
this to speed things up by creating data once before any example in a group is
run, however, this introduces a number of complications and you should only do
this if you have a firm grasp of the implications.

😦 I'm sorry the documentation on this isn't very clear. Additionally, I'm sorry that the helper method errors are not helpful at all.

The fixture data is already loaded in the database. You can access it via Widget.find though. In generally, we do not suggest modifying data in before(:context). Generally the reason people give is "speed" but this is often, not always, said before any actual speed measurements are taken. Since fixtures are loaded once at the start of the spec run, they already exist in the database, so you are not paying any database penalty by using them in a before(:each).

I'll ponder a few improvements, but it would really help to understand your need for a before(:context) usage over before(:example) here.

[mdesantis]

You're right, that is the problem. Anyway, I think it would be a better "developer experience" if the error could be catched by RSpec in order to give to the developer a more useful message... what do you think?

[cupakromer]

@mdesantis I fully agree. I already have a partial implementation for it. I will be pushing a PR in the next day or two with it.

[cupakromer]

The fixture data is already loaded in the database. You can access it via Widget.find though.

That actually is not true. If the data is available it is likely due to a previous fixture being loaded. The Active Record test fixtures do not delete themselves from the database at the end. They simply re-load prior to a test run. If you use transactions, changes are rolled back, but the fixtures are not dropped.

This means any changes you make will always get dropped before your example when you use fixtures.

[cupakromer]

Closing in favor of helper shims in #1208.