foo.rb spec - with bug

foo_spec_bug.rb

require_relative '../foo'

describe StatefulCalculator do
  before(:all) do
    @subject = StatefulCalculator.new
  end

  it 'should add some numbers' do
    expect(@subject.add(5).add(3).add(10).result).to eq(18)
  end
end

seeing_foo_spec_bug.rb

require_relative '../foo'

describe StatefulCalculator do
  before(:all) do
    @subject = StatefulCalculator.new
  end

  it 'should add some numbers' do
    expect(@subject.add(5).add(3).add(10).result).to eq(18)
  end

  it 'should divide some numbers' do
    expect(@subject.add(10).div(2).result).to eq(5) # Failure! Expected 5 and got 14
  end
end

stateless_foo_spec.rb

describe StatelessCalculator do
  it 'should add some numbers' do
    expect(StatelessCalculator.add(10, StatelessCalculator.add(5, 3))).to eq(18)
  end

  it 'should divide some numbers' do
    expect(StatelessCalculator.div(10, 2)).to eq(5)
  end
end