Log Capybara Exceptions

application.rb

# Note: Add the uncommented lines inside the Application class definition inside application.rb file

# [...]
# class XYZ < Rails::Application
  if Rails.env == 'test'
    require 'diagnostic'
    config.middleware.use(::Diagnostic)
  end

diagnostic.rb

# Note: Put this class in 'lib'

class Diagnostic
  FILENAME = File.join(Rails.root, 'log', 'test.log')

  def initialize(app)
    @app = app
  end

  def call(env)
    return @app.call(env)
  rescue StandardError => e
    trace = e.backtrace.select{ |l|l.start_with?(Rails.root.to_s) }.join("\n    ")
    msg = "#{e.class}\n#{e.message}\n#{trace}\n"
    File.open(FILENAME, 'a') { |f|
      f.write "\n"
      f.write "\n"
      f.write " ---   BACKTRACE   --- \n"
      f.write "\n"

      f.write msg

      f.write "\n"
      f.write " ---   BACKTRACE   --- \n"
      f.write "\n"
      f.write "\n"
    }
    raise e
  end
end

test.rb

# Note: Make sure this setting exist inside test.rb file

config.action_dispatch.show_exceptions = true