assertions.rb

# I noticed this syntax worked for multiple levels of modules so I tried it
module MiniTest::Assertions
  def assert_something_amazing
    true
  end
end

foo_test.rb

# test/integration/foo_test.rb

require '../test_helper'

class TestShell < Foo::Test::IntegrationTestCase

  def test_something_cool
    assert some_method
  end
end

test_helper.rb

# test/test_helper.rb

require 'minitest/autorun'

$:.unshift(File.join(File.dirname(__FILE__), '..', 'lib'))
$:.unshift(File.dirname(__FILE__))

require 'assertions'

module Foo
  module Test
    class IntegrationTestCase < Minitest::Test
      def some_method
        true
      end
    end
  end
end