Add spec for table formatting methods.
user
```ruby
require 'spec_helper'

module FatTable
  describe Table do
    describe 'output' do
      # These tests are taken from https://www.tutorialspoint.com/postgresql/postgresql_using_joins.htm
      before :all do
        @tab = Table.from_aoh([
          { id: 1, name: 'Paul', age: 32, address: 'California', salary: 20000, join_date: '2001-07-13' },
          { id: 3, name: 'Teddy', age: 23, address: 'Norway', salary: 20000},
          { id: 4, name: 'Mark', age: 25, address: 'Rich-Mond', salary: 65000, join_date: '2007-12-13' },
          { id: 5, name: 'David', age: 27, address: 'Texas', salary: 85000, join_date: '2007-12-13' },
          { id: 2, name: 'Allen', age: 25, address: 'Texas', salary: nil, join_date: '2007-12-13' },
          { id: 8, name: 'Paul', age: 24, address: 'Houston', salary: 20000, join_date: '2005-07-13' },
          { id: 9, name: 'James', age: 44, address: 'Norway', salary: 5000, join_date: '2005-07-13' },
          { id: 10, name: 'James', age: 45, address: 'Texas', salary: 5000, join_date: '2005-07-13' }
        ])
      end

      it 'should be able to output to aoa' do
        out = @tab.to_aoa
        expect(out.class).to eq(Array)
        expect(out.first.class).to eq(Array)
      end

      it 'should be able to output to aoh' do
        out = @tab.to_aoh
        expect(out.class).to eq(Array)
        expect(out.first.class).to eq(Hash)
      end

      it 'should be able to output to text' do
        out = @tab.to_text
        expect(out.class).to eq(String)
      end
    end
  end
end
```
assistant