rspec stub to allow [hash_key] to be passed

you can do this:

allow(menu.menu_items).to receive(:[]).and_return({Beer: 2.0})

You can also pass an specific item if you need:

allow(menu.menu_items).to receive(:[]).with(1).and_return({Beer: 2.0})

The line menu.menu_items[item] is in reality composed by 3 method calls. [] is a call to the method [] on the Hash returned by menu_items.

I assume menu.menu_items returns a Hash and not an Array, given in the spec item is a Symbol.

That means your stub requires a little bit more work.

allow(menu).to receive(:menu_items).and_return({ Beer: 2.0 })

Also note, the error

undefined local variable or method `item'

is because you were using item in the spec, but item is not defined outside your method.