```ruby
# frozen_string_literal: true

RSpec.describe RuboCop::Formatter::WorstOffendersFormatter do
  subject(:formatter) { described_class.new(output) }

  let(:output) { StringIO.new }

  let(:files) do
    %w[lib/rubocop.rb spec/spec_helper.rb exe/rubocop].map do |path|
      File.expand_path(path)
    end
  end

  describe '#finished' do
    context 'when there are many offenses' do
      let(:offense) { double('offense') }

      before do
        formatter.started(files)
        files.each_with_index do |file, index|
          formatter.file_finished(file, [offense] * (index + 2))
        end
      end

      it 'sorts by offense count first and then by cop name' do
        formatter.finished(files)
        expect(output.string).to eq(<<-OUTPUT.strip_indent)

          4  exe/rubocop
          3  spec/spec_helper.rb
          2  lib/rubocop.rb
          --
          9  Total

        OUTPUT
      end
    end
  end
end
```

Use verifying doubles in WorstOffendersFormatter spec
user
```ruby
# frozen_string_literal: true

RSpec.describe RuboCop::Formatter::WorstOffendersFormatter do
  subject(:formatter) { described_class.new(output) }

  let(:output) { StringIO.new }

  let(:files) do
    %w[lib/rubocop.rb spec/spec_helper.rb exe/rubocop].map do |path|
      File.expand_path(path)
    end
  end

  describe '#finished' do
    context 'when there are many offenses' do
      let(:offense) { instance_double(RuboCop::Cop::Offense) }

      before do
        formatter.started(files)
        files.each_with_index do |file, index|
          formatter.file_finished(file, [offense] * (index + 2))
        end
      end

      it 'sorts by offense count first and then by cop name' do
        formatter.finished(files)
        expect(output.string).to eq(<<-OUTPUT.strip_indent)

          4  exe/rubocop
          3  spec/spec_helper.rb
          2  lib/rubocop.rb
          --
          9  Total

        OUTPUT
      end
    end
  end
end
```
assistant