Minitest is a library that has been developed by the (some might say, infamous) Seattle Ruby community.

It has replaced the much older, and much more clunky, original test/unit, a library that used to be included in Ruby’s standard library. Nowadays, Ruby ships with the more modern, and more extensible, Minitest, so you can simply require it, and you’re good to go — you can start writing tests.

Minitest works much like our little Test library. Here’s an example taken straight from the project’s README, I’ve only shortened it a bit.

Given that you’d like to test the following class:

class Meme
  def i_can_has_cheezburger?

Define your tests as methods beginning with test_:

require "minitest/autorun"

class TestMeme < Minitest::Test
  def setup
    @meme =

  def test_that_kitty_can_eat
    assert_equal "OHAI!", @meme.i_can_has_cheezburger?

  def test_that_will_be_skipped
    skip "test this later"

As you can see there’s a method called setup. This method will be called before each of the test methods. This makes sense if you think about the stages that tests usually include: you want setup to be run first, before each of the tests.

Check out their documentation on what assertions are defined. There are assert, and assert_equal, much like the methods that we’ve defined before. But there also are a lot more useful methods, and most of them come with a counterpart method refute (fail if truthy, while assert fails if falsy).

Try to translate some of our manual tests in the chapter testing to Minitest.

In order to do so create a file that has your code (e.g. the method leap_year?), and then defines a class, e.g. LeapYearTest, that inherits from Minitest::Test. You’ll also want to require "minitest/autorun" at the very top of that file.

Also consider finding other code in the Ruby for Beginners book that looks like it should be tested, and try writing some tests for it.