Using RSpec expectations in MiniTest tests

rspec_test.rb

module RSpecTest
  include RSpec::Matchers

  def self.included(base)
    base.extend ClassMethods
  end

  def expect(*a, &b)
    # So number of assertions equals number of expectations in output
    assert(true)
    super
  end

  module ClassMethods
    def test(*args, &block)
      super(*args) do
        begin
          self.instance_eval(&block)
        rescue RSpec::Expectations::ExpectationNotMetError => e
          raise MiniTest::Assertion, e.message
        end
      end
    end
  end
end

some_test.rb

class SomeTest < ActiveSupport::TestCase
  include RSpecTest

  test 'it can use matchers' do
    expect(3).to eq(3)
  end
end