Prevent unrelated exceptions by requiring rails_helper at .rspec

When there is a bug in the code on the load,
RSpec catches the exception, aborts the spec file,
proceeds to the following spec file, and retries `require`
with partially loaded Rails application.

In some cases, we see many identical errors,
such as `NameError`, which are noisy but help developers
find the bug. In other cases, we see many unrelated errors,
typically `FrozenError` on finalized objects,
which push out the original exception raised only from the first spec.

The following comment describes this issue in detail.
thoughtbot/factory_bot_rails#303 (comment)

This patch prevents unrelated exceptions by the fail-fast feature.
rspec/rspec-core#2568

lib/generators/rspec/install/install_generator.rb

@@ -41,6 +41,9 @@ def generate_rspec_init(tmpdir)
 
         replace_generator_command(spec_helper_path)
         remove_warnings_configuration(spec_helper_path)
+
+        dot_rspec_path = File.join(tmpdir, '.rspec')
+        prepend_require_rails_helper_option(dot_rspec_path)
       end
 
       def replace_generator_command(spec_helper_path)
@@ -58,6 +61,12 @@ def remove_warnings_configuration(spec_helper_path)
                   '',
                   verbose: false
       end
+
+      def prepend_require_rails_helper_option(dot_rspec_path)
+        prepend_to_file dot_rspec_path,
+                        "--require rails_helper\n",
+                        verbose: false
+      end
     end
   end
 end

spec/generators/rspec/install/install_generator_spec.rb

@@ -47,11 +47,12 @@ def filter_rails_from_backtrace
 
   let(:rails_helper) { content_for('spec/rails_helper.rb') }
   let(:spec_helper) { content_for('spec/spec_helper.rb') }
+  let(:dot_rspec) { content_for('.rspec') }
   let(:developmentrb) { content_for('config/environments/development.rb')  }
 
   it "generates .rspec" do
     run_generator
-    expect(file('.rspec')).to exist
+    expect(dot_rspec).to match(/\A--require rails_helper\n/)
   end
 
   it "generates spec/spec_helper.rb" do