# encoding: utf-8

require 'spec_helper'

describe Algebra::Projection, '#each' do
  subject { object.each { |tuple| yields << tuple } }

  let(:object)   { described_class.new(relation, [:id])                  }
  let(:relation) { Relation.new([[:id, Integer], [:name, String]], body) }
  let(:body)     { [[1, 'Dan Kubb'], [2, 'Dan Kubb'], [2, 'Alex Kubb']]  }
  let(:yields)   { []                                                    }

  it_should_behave_like 'an #each method'

  it 'yields only tuples' do
    subject
    yields.each { |tuple| tuple.should be_instance_of(Tuple) }
  end

  it 'yields only tuples with the expected header' do
    subject
    yields.each { |tuple| tuple.header.should be(object.header) }
  end

  it 'yields only tuples with the expected data' do
    expect { subject }.to change { yields.dup }
      .from([])
      .to([[1], [2]])
  end
end