Sounds like it should work as is, assuming the implementation is something like this:

```ruby
class MockLogger
  attr_accessor :messages, :errors

  def initialize
    @messages = []
    @errors = []
  end

  %w(debug info warn).each do |level|
    class_eval <<-RUBY1
      def #{level}(msg)
        @messages << msg
      end
    RUBY1
  end
  
  %w(error fatal).each do |level|
    class_eval <<-RUBY2
      def #{level}(msg)
        @messages << msg
        @errors << msg
      end
    RUBY2
  end
end

```