# encoding: utf-8 require 'spec_helper' describe Algebra::Product, '#delete' do subject { object.delete(other) } let(:object) { described_class.new(left, right) } let(:other) { double('other') } let(:left) { Relation.new([[:id, Integer]], [[1]]) } let(:right) { Relation.new([[:name, String]], [['John Doe']]) } specify { expect { subject }.to raise_error(ImmutableRelationError, 'deleting from a product is impossible') } end