bar_test.rb

describe FooCommand do 
  
  it 'sets the name of and saves bar' do
    # setup
    foo_command = FooCommand.as_subject
    # store is wired onto every test, and shared by the DAO class Save / Find etc.    
    store.put(Bar.new(id: 123, name: 'old_name'))
    
    
    #exercise
    foo_command.(123, "Bar")
    
    #assert
    saved_bar = store.get(Bar, 123)
    assert saved_bar.name == "Bar"
  end
  
end

foo_command.rb

class FooCommand < Commands::Command
  
  dependency :find, Queries::Id.klass(Baz)
  dependency :save, Commands::SaveRecord
  
  def call(bar_id, bar_name)
    bar = find.(bar)
    bar.name = bar_name
    save.(bar)
    
    bar
  end
  
end