# encoding: utf-8 require 'spec_helper' describe Aggregate::Variance, '.finalize' do subject { object.finalize(accumulator) } let(:object) { described_class } let(:accumulator) { [ count, mean, sum_of_squares ] } context 'when the count is 0' do let(:count) { 0 } let(:mean) { 1 } let(:sum_of_squares) { 1 } it { should be_nil } end context 'when the count is not 0' do let(:count) { 6 } let(:mean) { 3.5 } let(:sum_of_squares) { 17.5 } it { should be_within(2.91).of(0.01) } end end