Add tests for table and renderer integration.
user
```ruby
# -*- encoding: utf-8 -*-

require 'spec_helper'

describe TTY::Table, '#to_s' do
  let(:header) { ['h1', 'h2', 'h3'] }
  let(:rows) { [['a1', 'a2', 'a3'], ['b1', 'b2', 'b3']] }
  let(:renderer) { :basic }

  subject { described_class.new header, rows, :renderer => renderer }

  context 'without border' do
    it 'displays table' do
      subject.to_s.should == <<-EOS.normalize
        h1 h2 h3
        a1 a2 a3
        b1 b2 b3
      EOS
    end
  end

  context 'with ascii border' do
    let(:renderer) { :ascii }

    it 'displays table' do
      subject.to_s.should == <<-EOS.normalize
        +---+---+--+
        |h1 |h2 |h3|
        +---+---+--+
        |a1 |a2 |a3|
        |b1 |b2 |b3|
        +---+---+--+
      EOS
    end
  end

  context 'with unicode border' do
    let(:renderer) { :unicode}

    it 'displays table' do
      subject.to_s.should == <<-EOS.normalize
        ┌───┬───┬──┐
        │h1 │h2 │h3│
        ├───┼───┼──┤
        │a1 │a2 │a3│
        │b1 │b2 │b3│
        └───┴───┴──┘
      EOS
    end
  end
end
```
assistant