Compare version numbers with pessimistic constraints http://shorts.jeffkreeftmeijer.com/2014/compare-version-numbers-with-pessimistic-constraints/

## version.rb
class Version
  include Comparable
  attr_reader :major, :minor, :patch

  def initialize(number)
    @major, @minor, @patch = number.split('.').map(&:to_i)
  end

  def to_a
    [major, minor, patch].compact
  end

  def <=>(version)
    (major.to_i <=> version.major.to_i).nonzero? ||
    (minor.to_i <=> version.minor.to_i).nonzero? ||
    patch.to_i <=> version.patch.to_i
  end

  def matches?(operator, number)
    version = Version.new(number)

    return self == version if operator == '='
    return self > version  if operator == '>'
    return self < version  if operator == '<'
    return version <= self && version.next > self if operator  == '~>'
  end

  def next
    next_version = to_a

    if next_version.length == 1
      next_version[0] += 1
    else
      next_version[-2] += 1
      next_version[-1] = 0
    end

    Version.new(next_version.join('.'))
  end
end

## version_test.rb
require 'minitest/autorun'
require_relative 'version'

describe Version do
  before do
    @version = Version.new('1.2.0')
  end

  it "has a major version number" do
    assert @version.major, 1
  end

  it "has a minor version number" do
    assert @version.minor, 2
  end

  it "has a patch level version number" do
    assert @version.patch, 0
  end

  it "is equal" do
    assert @version == Version.new('1.2.0')
  end

  describe "concerning comparisons" do
    it "compares major version numbers" do
      assert Version.new('2') > Version.new('1')
      assert Version.new('1') < Version.new('2')
    end

    it "compares minor version numbers" do
      assert Version.new('1.2') > Version.new('1.1')
      assert Version.new('1.1') < Version.new('1.2')
    end

    it "compares patch level version numbers" do
      assert Version.new('1.1.2') > Version.new('1.1.1')
      assert Version.new('1.1.1') < Version.new('1.1.2')
    end
  end

  describe "concerning version matching" do
    it "matches versions with the '=' operator" do
      assert Version.new('1.2.0').matches?('=', '1.2.0')
      assert Version.new('1.2.0').matches?('=', '1.2')
      assert !Version.new('1.2.0').matches?('=', '1.1')
    end

    it "matches versions with the '>' operator" do
      assert Version.new('1.1').matches?('>', '1.0')
      assert !Version.new('1.0').matches?('>', '1.0')
      assert !Version.new('1.0').matches?('>', '1.1')
    end

    it "matches versions with the '<' operator" do
      assert Version.new('1.0').matches?('<', '1.1')
      assert !Version.new('1.0').matches?('<', '1.0')
      assert !Version.new('1.1').matches?('<', '1.0')
    end

    it "matches versions with the '~>' operator" do
      assert Version.new('1.0').matches?('~>',  '1')
      assert Version.new('1.0').matches?('~>',  '1.0')
      assert Version.new('1.0').matches?('~>',  '1.0.0')
      assert Version.new('1.1').matches?('~>',  '1')
      assert Version.new('1.1').matches?('~>',  '1.0')
      assert !Version.new('1.1').matches?('~>',  '1.0.0')
    end
  end
end