```ruby
$LOAD_PATH << File.expand_path('../../lib', __FILE__)
$LOAD_PATH << File.expand_path('../../spec/helpers', __FILE__)
require 'buildpack/packager'
require 'file_system_helpers'

RSpec.configure do |config|
  config.include FileSystemHelpers
end
```

Check for existence of `tree` before running suite.
user
```ruby
$LOAD_PATH << File.expand_path('../../lib', __FILE__)
$LOAD_PATH << File.expand_path('../../spec/helpers', __FILE__)
require 'buildpack/packager'
require 'file_system_helpers'

unless system("which tree")
  raise "Please install the `tree` commandline tool."
end

RSpec.configure do |config|
  config.include FileSystemHelpers
end
```
assistant