Design a spreadsheet engine in Ruby

spreadsheet-test.rb

require 'spreadsheet'
require 'minitest/autorun'

class TestSpreadsheet < MiniTest::Test
  def setup
    @sheet = Spreadsheet.new([2,2], "Sheet")
  end
  
  def test_for_iniatialize
    assert_equal(2, @sheet.rows)
    assert_equal(2, @sheet.cols)
    assert_equal("Sheet", @sheet.title)
  end
  
  def test_for_cell
    foo = @sheet.cell([0,0],"Foo")

    assert_equal("Foo", foo)  # method return value 
    assert_equal("Foo", @sheet.cell([0,0]))  # accessing cell
    assert_nil(@sheet.cell([0,1]))

    assert_raises(IndexError) do
      @sheet.cell([3,0])
    end
    assert_raises(IndexError) do
      @sheet.cell([0,3])
    end
  end

end

spreadsheet.rb

class Spreadsheet
  
  attr_reader :rows, :cols, :data
  attr_accessor :title

  def initialize(dimensions = [], title = nil)
    rows = dimensions[0]
    cols = dimensions[1]
  
    @data = Array.new(rows) { Array.new(cols) }
    @title = title
  end
  
  def rows
    @data.size
  end
  
  def cols
    @data[0].size
  end
  
  def cell(position, value = nil)
    row = position[0]
    col = position[1]
    
    raise IndexError if row > @data.size or col > @data[row].size
    
    if value
      @data[row][col] = value  # set
    else
      value = @data[row][col]  # get
    end
    return value
  end
  
end