`ruby -Itest example_test.rb`

example.rb

# frozen_string_literal: true

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end
gemfile(true) do
  source 'https://rubygems.org'
  git_source(:github) { |repo| "https://github.com/#{repo}.git" }
  ruby '2.7.2'

  gem 'rails', github: 'rails/rails', require: true
  gem 'graphql', require: true
  gem 'pry-byebug', require: true
  gem 'mocha', require: true
  gem 'minitest', require: true
end

class MyComplexLogicService
  def self.do_stuff
    {id: 1}
  end
end

module Types
  class Bar < GraphQL::Schema::Object
    field :id, Integer, null: true
  end

  class Query < GraphQL::Schema::Object
    field :bar, Bar, null: true

    def bar
      MyComplexLogicService.do_stuff
    end
  end
end

class ZoomSchema < GraphQL::Schema
  query(Types::Query)
end

example_test.rb

# frozen_string_literal: true

require_relative './example'
require 'minitest/autorun'
require 'mocha/minitest'

class ExampleTest < Minitest::Test
  def test_my_complex_logic_service
    result = MyComplexLogicService.do_stuff

    expected_result = {id: 1}
    assert_equal(expected_result, result)
  end

  def test_bar_query
    query_string = <<~QUERY
      query {
        bar {
          id
        }
      }
    QUERY

    MyComplexLogicService.expects(:do_stuff).returns({id: 1})

    result = ZoomSchema.execute(query_string).to_h

    expected_result = {
      "data" => {
        "bar" => {
          "id" => 1
        }
      }
    }

    assert_nil(result['errors'])
    assert_equal(expected_result, result)
  end
end