Beter way to test if method is called x times with MiniTest?

Today I've started with some basic implementation of minitest and finally figured a way out to test if a method on a class is called twice.

In RSpec I would do something like:

expect(@foo).to receive(:some_heavy_calculation).twice
@foo.bar

Now, I've came up with the following implementation for MiniTest, but I'm not sure if this is the way to implement this, because this. Here's what I've got

require 'minitest/autorun'

class Foo
  def bar
    @cached_value ||= some_heavy_calculation
  end

  def some_heavy_calculation
    "result"
  end
end

class FooTest < Minitest::Test
  def setup
    @foo = Foo.new
  end

  def cache_the_value_when_calling_bar_twice
    mock = Minitest::Mock.new
    mock.expect(:some_heavy_calculation, [])
    @foo.stub :some_heavy_calculation, -> { mock.some_heavy_calculation } do
      2.times { assert_equal_set @foo.bar, [] }
    end
    mock.verify
  end
end

Do I really have to implement this with a mock, which will be the result of the stub of the subject on the method that has to be called x times?