Use Minitest one-line pattern matching assert in Ruby

If you haven’t written Ruby tests using Minitest in a while, you might have missed the addition of the assert_pattern assertion (available in Ruby 3.0 and higher). Right now, it’s my absolute favorite assertion when I need to validate a complex object-like an array or a hash-in a single go. Of course, there is one limitation when checking hashes: keys can only be symbols. So if you want to validate JSON, you’ll need to transform its keys from strings to symbols first.

require 'json'
require 'minitest'

class ExampleTest < Minitest::Test
  def test_example_array_assert_pattern
    xs = Array.new(3) { rand(100) }

    assert_pattern { xs => [Integer, Integer, Integer] }
  end

  def test_example_hash_assert_pattern
    h = JSON.parse(
      '{"id":1,"name":"Artem","busy":true,"langs":["Ruby","Rust"]}'
    )
    h = h.transform_keys(&:to_sym)
    lang = 'Ruby'

    assert_pattern do
      h => {
        id: Integer,
        name: String,
        busy: TrueClass | FalseClass,
        langs: [^lang, *]
      }
    end
  end
end

Minitest.run # Explicitly running tests in IRB

Have you had any experience using assert_pattern? What are your favorite Minitest assertions to use in projects?