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
    its(:test, :os => :windows) { should == :windows }
    its(:test, :os => :linux)   { should == :linux   }
    its(:test, :os => :macosx)  { should == :macosx  }
    its(:test, :os => :unix)    { should == :unix    }
  end

end