undefined function error in rspec

I am having trouble running an rspec file, provided as part of an exercise, and I am not sure what is going on.

Here is my code in silly_blocks.rb:

def reverser(num = 1)
  result = []
  if yield == Integer
    yield + num
  else
    yield.split.each{|word| result << word.reverse}  
  result.join(' ')

  end

end

Here is the rspec file:

require "05_silly_blocks"

describe "some silly block functions" do

  describe "reverser" do
    it "reverses the string returned by the default block" do
      result = reverser do
        "hello"
      end
      result.should == "olleh"
    end

    it "reverses each word in the string returned by the default block" do
      result = reverser do
        "hello dolly"
      end
      result.should == "olleh yllod"
    end
  end

  describe "adder" do
    it "adds one to the value returned by the default block" do
      adder do
        5
      end.should == 6
    end

    it "adds 3 to the value returned by the default block" do
      adder(3) do
        5
      end.should == 8
    end
  end

  describe "repeater" do
    it "executes the default block" do
      block_was_executed = false
      repeater do
        block_was_executed = true
      end
      block_was_executed.should == true
    end

    it "executes the default block 3 times" do
      n = 0
      repeater(3) do
        n += 1
      end
      n.should == 3
    end

    it "executes the default block 10 times" do
      n = 0
      repeater(10) do
        n += 1
      end
      n.should == 10
    end

  end

end

I get this error when it hits the third test 'adder':

Failures:                                                                                                                                  

  1) some silly block functions adder adds one to the value returned by the default block                                                  
     Failure/Error: adder do                                                                                                               
     NoMethodError:                                                                                                                        
       undefined method `adder' for #<RSpec::ExampleGroups::SomeSillyBlockFunctions::Adder:0x007f334345b460>                               
     # ./p.rb:30:in `block (3 levels) in <top (required)>' 

It seems that adder was defined in the exact same way as previous methods in the rspec, so I am not sure what is going on. I have check various other posts about this but haven't found anything to help me, or at least that I understand enough to help me.