Take an already instantiated obj and make it a null_object for the duration of a single test

gistfile1.rb

  describe '#put_resource!' do

    before(:each) do
      @c = Converter.new name: 'c'
      @edge_in = double(from: double(), to: @c)
      @edge_out = double(from: @c, to: double())
      @c.attach_edge!(@edge_out).attach_edge!(@edge_in)
    end

    it 'does not ping incoming edges' do

      expect(@edge_in).not_to receive(:test_ping?)
      @edge_out.as_null_object
      @c.put_resource!(double())

    end