```ruby
require 'rspec/given'
require 'subtime/timer'
require 'kernel/kernel'

describe Timer do

  let(:timer_output) { double('timer_output').as_null_object }

  describe "#start" do
    context "without messages" do
      let(:minutes) { 0 }
      let(:timer) { Timer.new(timer_output, minutes) }

      it "outputs 'Starting timer for 0 minutes...'" do
        expect(timer_output).to receive(:puts).with("Starting timer for #{minutes} minutes...")

        timer.start
      end
    end

    context "for 10 minutes with code blocks" do
      let(:minutes) { 10 }
      let(:messages) { { 5 => lambda { puts "Something" },
                         2 => lambda { puts "something else" } } }
      let(:timer) { Timer.new(timer_output, minutes, messages) }

      it "outputs 'Starting timer for 10 minutes...'" do
        expect(timer_output).to receive(:puts).with("Starting timer for #{minutes} minutes...")

        timer.start
      end

      it "outputs each minute from 10 down to 1" do
        10.downto(1) do |minute|
          expect(timer_output).to receive(:puts).with(minute)
        end

        timer.start
      end

      it "calls the specified code blocks" do
        expect { timer.start }.to output(/Something/).to_stdout
        expect { timer.start }.to output(/something else/).to_stdout
      end
    end
  end
end
```

Add override for $stdout to make rspec output pretty
user
```ruby
require 'rspec/given'
require 'subtime/timer'
require 'kernel/kernel'

describe Timer do

  before do
    $stdout = StringIO.new
  end

  let(:timer_output) { double('timer_output').as_null_object }

  describe "#start" do
    context "without messages" do
      let(:minutes) { 0 }
      let(:timer) { Timer.new(timer_output, minutes) }

      it "outputs 'Starting timer for 0 minutes...'" do
        expect(timer_output).to receive(:puts).with("Starting timer for #{minutes} minutes...")

        timer.start
      end
    end

    context "for 10 minutes with code blocks" do
      let(:minutes) { 10 }
      let(:messages) { { 5 => lambda { puts "Something" },
                         2 => lambda { puts "something else" } } }
      let(:timer) { Timer.new(timer_output, minutes, messages) }

      it "outputs 'Starting timer for 10 minutes...'" do
        expect(timer_output).to receive(:puts).with("Starting timer for #{minutes} minutes...")

        timer.start
      end

      it "outputs each minute from 10 down to 1" do
        10.downto(1) do |minute|
          expect(timer_output).to receive(:puts).with(minute)
        end

        timer.start
      end

      it "calls the specified code blocks" do
        expect { timer.start }.to output(/Something/).to_stdout
        expect { timer.start }.to output(/something else/).to_stdout
      end
    end
  end
end
```
assistant