Strange concurrent-ruby test behaviour

strangeness.rb

#!/usr/bin/env ruby

require 'test/unit'
require 'concurrent'

Concurrent::Future.execute { 5 * 5 }.value # => Works

class SanityTest < Test::Unit::TestCase
  def test_my_sanity
    assert_equal(Concurrent::Future.execute { 5 * 5 }.value, 25) # => Doesn't work
  end
end