using print inside def having yield statement

I am trying to print inside a function. The function is used for invoking a block. But I don't see the print happening in the function definition. Please shed a light on this. Basically I am not clear with the control flow.

def find_all 
   matching_items = [] 

   self.each do |item|

      if yield(item)
         puts "after yield" #print not happening
         matching_items << item
      end
   end

   matching_items

end

p ['a', 'b','c','c'].find_all { |item| 
  if item == 'a'
     true 
  end   
  } 

If you are trying to re-open the class Array then, this is how you can do it

class Array
  def find_all(matching_items = [])
    self.each do |item|
      if yield(item)
        puts "after yield" #print not happening
        matching_items << item
      end
    end
    matching_items
  end
end

p ['a', 'b', 'c', 'c'].find_all { |item|
    if item == 'a'
      true
    end
  }

Output

after yield
["a"]