Warn if a fixture method is called from a before(:context) block.

Changelog.md

@@ -5,6 +5,8 @@ Bug fixes:
 
 * Make it possible to write nested specs within helper specs on classes that are
   internal to helper classes. (Sam Phippen, Peter Swan, #1499).
+* Warn if a fixture method is called from a `before(:context)` block, instead of
+  crashing with a `undefined method for nil:NilClass`. (Sam Phippen, #1501)
 
 ### 3.4.0 / 2015-11-11
 [Full Changelog](http://github.com/rspec/rspec-rails/compare/v3.3.3...v3.4.0)

example_app_generator/generate_stuff.rb

@@ -14,6 +14,7 @@ def setup_tasks
 
     def final_tasks
       copy_file 'spec/verify_active_record_spec.rb'
+      copy_file 'spec/verify_fixture_warning_spec.rb'
       run('bin/rake db:migrate')
       if ::Rails::VERSION::STRING.to_f < 4.1
         run('bin/rake db:migrate RAILS_ENV=test')

example_app_generator/spec/verify_fixture_warning_spec.rb

@@ -0,0 +1,64 @@
+require 'rails_helper'
+
+RSpec.describe "Fixture warnings" do
+  def generate_fixture_example_group(hook_type)
+    RSpec.describe do
+      include RSpec::Rails::RailsExampleGroup
+      fixtures :things
+
+      before(hook_type) do
+        things :a
+      end
+
+      it "" do
+
+      end
+    end
+  end
+
+  it "Warns when a fixture call is made in a before :context call" do
+    expect(RSpec).to receive(:warn_with).with(match(/Calling fixture method in before :context/))
+
+    generate_fixture_example_group(:context).run
+  end
+
+  it "Does not warn when a fixture call is made in a before :each call" do
+    expect(RSpec).not_to receive(:warn_with)
+
+    generate_fixture_example_group(:each).run
+  end
+
+end
+
+RSpec.describe "Global fixture warnings" do
+  def generate_fixture_example_group(hook_type)
+    RSpec.describe do
+      include RSpec::Rails::RailsExampleGroup
+
+      before(hook_type) do
+        things :a
+      end
+
+      it "" do
+
+      end
+    end
+  end
+  around do |ex|
+    RSpec.configuration.global_fixtures = [:things]
+    ex.call
+    RSpec.configuration.global_fixtures = []
+  end
+
+  it "warns when a global fixture call is made in a before :context call" do
+    expect(RSpec).to receive(:warn_with).with(match(/Calling fixture method in before :context/))
+
+    generate_fixture_example_group(:context).run
+  end
+
+  it "does not warn when a global fixture call is made in a before :each call" do
+    expect(RSpec).not_to receive(:warn_with)
+
+    generate_fixture_example_group(:each).run
+  end
+end

lib/rspec/rails/fixture_support.rb

@@ -28,6 +28,28 @@ module FixtureSupport
             self.use_transactional_fixtures = RSpec.configuration.use_transactional_fixtures
           end
           self.use_instantiated_fixtures  = RSpec.configuration.use_instantiated_fixtures
+
+          def self.fixtures(*args)
+            orig_methods = private_instance_methods
+            super.tap do
+              new_methods = private_instance_methods - orig_methods
+              new_methods.each do |method_name|
+                proxy_method_warning_if_called_in_before_context_scope(method_name)
+              end
+            end
+          end
+
+          def self.proxy_method_warning_if_called_in_before_context_scope(method_name)
+            orig_implementation = instance_method(method_name)
+            define_method(method_name) do |*args, &blk|
+              if inspect.include?("before(:context)")
+                RSpec.warn_with("Calling fixture method in before :context ")
+              else
+                orig_implementation.bind(self).call(*args, &blk)
+              end
+            end
+          end
+
           fixtures RSpec.configuration.global_fixtures if RSpec.configuration.global_fixtures
         end
       end