require 'spec_helper'

Let me add `require 'spec_helper'`, otherwise, running tests for a specific file fails, for example

```
$ bundle exec rspec spec/config/config_parser_spec.rb
Failures:

  1) Fluent::Config::V1Parser @include parsing parses @include / include correctly
     Failure/Error: Fluent::Config::V1Parser.parse(data, File.basename(path), File.dirname(path))
     NoMethodError:
       private method `warn' called for nil:NilClass
     # ./lib/fluent/config/v1_parser.rb:97:in `parse_element'
     # ./lib/fluent/config/v1_parser.rb:41:in `parse!'
     # ./lib/fluent/config/v1_parser.rb:31:in `parse'
     # ./spec/config/config_parser_spec.rb:14:in `read_config'
     # ./spec/config/config_parser_spec.rb:311:in `block (3 levels) in <top (required)>'
```

This makes me feel bad to do TDD.