test.rb

#!/usr/bin/env ruby

require 'serverspec'

class Foo
  include Serverspec

  def command(cmd)
    self.class.command(cmd)
  end

  def user(user)
    self.class.user(user)
  end

  def self.command(cmd)
    describe 'command' do
      it "command: #{cmd}" do
        expect((command cmd).exit_status).to eq 0
      end
    end
  end

  def self.user(user)
    describe 'user' do
      it 'user' do
        expect(user user).to exist
      end
    end
  end
end

set :backend, :exec
f = Foo.new
f.command('ls')
f.command('ls /tmp')
f.user('rooot')

test2.rb

#!/usr/bin/env ruby

require 'serverspec'

class Foo
  def command(cmd)
    Serverspec.describe 'command' do
      it "command: #{cmd}" do
        expect((command cmd).exit_status).to eq 0
      end
    end
  end

  def user(user)
    Serverspec.describe 'user' do
      it 'user' do
        expect(user user).to exist
      end
    end
  end
end

set :backend, :exec
f = Foo.new
f.command('ls')
f.command('ls /tmp')
f.user('rooot')