```ruby
require File.expand_path('../support/helpers', __FILE__)

describe 'hadoop::hadoop_hdfs_datanode' do

  include Helpers::Hadoop

  # Example spec tests can be found at http://git.io/Fahwsw
  it 'runs no tests by default' do
  end

end
```

Add test on HDFS data dir
user
```ruby
require File.expand_path('../support/helpers', __FILE__)

describe 'hadoop::hadoop_hdfs_datanode' do

  include Helpers::Hadoop

  it 'ensures HDFS data dirs exist' do
    node['hadoop']['hdfs_site']['dfs.data.dir'].each do |dir|
      directory(dir)
      .must_exist
      .with(:owner, 'hdfs')
      .and(:group, 'hdfs')
      .and(:mode, node['hadoop']['hdfs_site']['dfs.datanode.data.dir.perm'])
  end

end
```
assistant