Fix tests and rename request variable in specs to perform_request

Explanation: Using the variable name `request` might interfere with methods in Rails core system prevent successful test execution. See this issue: https://github.com/turbolinks/turbolinks-rails/issues/38

spec/factories/code_ocean/error.rb

@@ -0,0 +1,6 @@
+FactoryBot.define do
+  factory :error, class: CodeOcean::Error do
+    association :execution_environment, factory: :ruby
+    message { "exercise.rb:4:in `<main>': undefined local variable or method `foo' for main:Object (NameError)" }
+  end
+end