RSpec.describe Mutest::Parallel do describe '.async' do subject { described_class.async(config) } let(:config) { instance_double(Mutest::Parallel::Config, env: env) } let(:env) { instance_double(Mutest::Actor::Env, new_mailbox: mailbox) } let(:mailbox) { Mutest::Actor::Mailbox.new } let(:master) { instance_double(Mutest::Parallel::Master) } before do expect(described_class::Master).to receive(:call).with(config).and_return(master) end it { is_expected.to eql(described_class::Driver.new(mailbox.bind(master))) } end end