json.rb

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"
  gem "minitest"
  gem "json", ENV.fetch("JSON", "2.7.2")
end
require "minitest/autorun"

puts "json: #{JSON::VERSION}"

class JSONGeneratorTest < Minitest::Test
  module CustomToJSON
    def to_json(*)
      %{"#{self.class.name}#to_json"}
    end
  end

  module CustomToS
    def to_s
      "#{self.class.name}#to_s"
    end
  end

  class ArrayWithToJSON < Array
    include CustomToJSON
  end

  def test_array_subclass_with_to_json
    assert_equal '"JSONGeneratorTest::ArrayWithToJSON#to_json"', JSON.generate(ArrayWithToJSON.new)
    assert_equal '{"[]":1}', JSON.generate(ArrayWithToJSON.new => 1)
  end

  class ArrayWithToS < Array
    include CustomToS
  end

  def test_array_subclass_with_to_s
    assert_equal '[]', JSON.generate(ArrayWithToS.new)
    assert_equal '{"JSONGeneratorTest::ArrayWithToS#to_s":1}', JSON.generate(ArrayWithToS.new => 1)
  end

  class HashWithToJSON < Hash
    include CustomToJSON
  end

  def test_hash_subclass_with_to_json
    assert_equal '"JSONGeneratorTest::HashWithToJSON#to_json"', JSON.generate(HashWithToJSON.new)
    assert_equal '{"{}":1}', JSON.generate(HashWithToJSON.new => 1)
  end

  class HashWithToS < Hash
    include CustomToS
  end

  def test_hash_subclass_with_to_s
    assert_equal '{}', JSON.generate(HashWithToS.new)
    assert_equal '{"JSONGeneratorTest::HashWithToS#to_s":1}', JSON.generate(HashWithToS.new => 1)
  end

  class StringWithToJSON < String
    include CustomToJSON
  end

  def test_string_subclass_with_to_json
    assert_equal '"JSONGeneratorTest::StringWithToJSON#to_json"', JSON.generate(StringWithToJSON.new)
    assert_equal '{"":1}', JSON.generate(StringWithToJSON.new => 1)
  end

  class StringWithToS < String
    include CustomToS
  end

  def test_string_subclass_with_to_s
    assert_equal '""', JSON.generate(StringWithToS.new)
    assert_equal '{"JSONGeneratorTest::StringWithToS#to_s":1}', JSON.generate(StringWithToS.new => 1)
  end
end