Testing

A Carton has two kinds of test. An integration test imports the Carton and sees only its Public Surface. A unit test loads the Carton’s files with plain require and can reach its private code.

Integration tests

Tests run in the Main Box, so a test imports a Carton the same way an app does. Run them with RUBY_BOX=1.

require 'minitest/autorun'
require 'carton'

class MathTest < Minitest::Test
  def setup
    @math = import_relative '../lib/math' # the Carton's export, nothing more
  end

  def test_add
    assert_equal 5, @math.add(2, 3)
  end
end

• Imports are shared across the process, so a Carton’s state persists from one test to the next. Keep Cartons stateless, or reset their state through their Public Surface.
• Files inside a Carton cannot be imported on their own, and private constants stay private across the boundary.

Unit tests

A Carton’s files are ordinary Ruby. Outside an import, export declares nothing, so require loads an Entrypoint into the test’s own Box like any other file. A unit test can then test code the Carton keeps private, and needs no RUBY_BOX=1:

require 'carton' # defines export, which does nothing here
require 'minitest/autorun'
require 'pricing' # plain require: no import, no boundary

class PricingTest < Minitest::Test
  # Pricing::Rounding raises NameError; const_get still returns it.
  Rounding = Pricing.const_get(:Rounding)

  def test_cents
    assert_equal BigDecimal('1.01'), Rounding.cents(BigDecimal('1.005'))
  end
end

• Keep unit and integration tests in separate files, and run each file in its own process. A plain require loads a second copy of the Carton beside the imported one.
• Private code can stay private instead of moving into a Carton of its own. A test names it once with const_get, or send for a private method, so each reach into private code is easy to find.

The monorepo example’s tests have both kinds.