gistfile1.rb

require 'rubygems'
require 'rbconfig'
require 'rspec'

class PlatformDependentExample
  def platform
    case RbConfig::CONFIG['host_os']
    when /windows/
      :windows
    when /linux/
      :linux
    when /darwin/
      :macosx
    when /solaris|bsd/
      :unix
    end
  end

  def test
    platform
  end
end

RSpec.configuration.filter_run :os => :linux

describe PlatformDependentExample do

  describe '#test' do
    before :all do
      @e = PlatformDependentExample.new
    end

    context 'Some subfeature that only exists on Linux', :os => :linux do
      it 'returns :linux' do
        @e.test.should == :linux
      end
    end
  end
  
end