phpspec. checking key for array

phpspec. checking key for array

Exist some class:
class A{
protected $options;
public function setDefaults($defaults){
$this->options=$defaults;
}
public function getOptions(){
return $this->options;
}
}
And other class:
class B{
public function setDefaultOptions(A $options){
$options->setDefaults('foo'=>'bar')
}
}
Uses:
$a=new A();
$b=new B();
$b->setDefaultsOptions(a);
How I can check in spec for B that $a->options['foo'] is set?