example.rb

class Example
  attr_reader :value

  def initialize(value)
    @value = value
  end

  def truthy?
    !!@value
  end

  def falsy?
    not truthy?
  end
end

rspec.rb

require_relative 'example'

describe Example do
  let(:value) { "value" }
  subject { Example.new(value) }

  it "should have value of the value" do
    subject.value.should == value
  end

  its(:truthy?) { should be }
  its(:falsy?) { should_not be }
end

spec.rb

require 'minitest/autorun'
require_relative 'example'

# Specifikace

describe Example, "example with value" do
  let(:value) { "value" }
  subject { Example.new(value) }

  describe "when asked about the value" do
    it "should be the value" do
      subject.value.must_equal value
    end
  end

  it "should be truthy" do
    subject.truthy?.must_equal true
  end

  it "should not be falsy" do
    subject.falsy?.wont_equal true
  end
end

test.rb

require 'minitest/autorun'
require_relative 'example'

# Unit test

class TestExample < MiniTest::Unit::TestCase
  def setup
    @value = "value"
    @example = Example.new(@value)
  end

  def test_value_will_return_value
    assert_equal @value, @example.value
  end

  def test_it_is_truthy
    assert @example.truthy?
  end

  def test_it_isnt_falsy
    refute @example.falsy?
  end
end