group :development, :test do
  gem 'dns_mock', require: false
end

# Example of mocked DNS records, please follow this data structure

records = {
  'example.com' => {
    a: %w[1.1.1.1 2.2.2.2],
    aaaa: %w[2a00:1450:4001:81e::200e],
    ns: %w[ns1.domain.com ns2.domain.com],
    mx: %w[mx1.domain.com mx2.domain.com:50], # you can specify host(s) or host(s) with priority, use '.:0' for definition null MX record
    txt: %w[txt_record_1 txt_record_2],
    cname: 'mañana.com', # you can specify hostname in UTF-8. It will be converted to xn--maana-pta.com automatically
    soa: [
      {
        mname: 'dns1.domain.com',
        rname: 'dns2.domain.com',
        serial: 2_035_971_683,
        refresh: 10_000,
        retry: 2_400,
        expire: 604_800,
        minimum: 3_600
      }
    ]
  },
  '1.2.3.4' => { # You can define RDNS host address without lookup prefix. It will be converted to 4.3.2.1.in-addr.arpa automatically
    ptr: %w[domain_1.com domain_2.com]
  },
  '_sip._tcp.example.com' => { # Please use {_service._proto.domain} pattern to follow the valid RFC-2782 SRV host pattern representation
    srv: [
      {
        priority: 0,
        weight: 10,
        port: 5_060,
        target: 'domain.com'
      }
    ]
  }
}

# Public DnsMock interface
# records:Hash, port:Integer, exception_if_not_found:Boolean
# are optional params. By default creates dns mock server with
# empty records. A free port for server will be randomly assigned
# in the range from 49152 to 65535, if record not found exception
# won't raises. Please note if you specify zero port number,
# free port number will be randomly assigned as a server port too.
# Returns current dns mock server
dns_mock_server = DnsMock.start_server(records: records) # => DnsMock::Server instance

# returns current dns mock server port
dns_mock_server.port # => 49322

# returns current collected server lookup messsages
# represented as array of Resolv::DNS::Message instances
dns_mock_server.messages # => [#<Resolv::DNS::Message>]

# interface to setup mock records.
# Available only in case when server mocked records is empty
dns_mock_server.assign_mocks(records) # => true/nil

# interface to reset current mocked records
dns_mock_server.reset_mocks! # => true

# interface to clear collected lookup messages
dns_mock_server.clear_messages! # => true

# interface to stop current dns mock server
dns_mock_server.stop! # => true

# returns list of running dns mock servers
DnsMock.running_servers # => [DnsMock::Server instance]

# interface to stop all running dns mock servers
DnsMock.stop_running_servers! # => true

# Gemfile

group :test do
  gem 'rspec'
  gem 'dns_mock', require: 'dns_mock/test_framework/rspec'
end

# spec/support/config/dns_mock.rb

require 'dns_mock/test_framework/rspec'

# spec/support/config/dns_mock.rb

RSpec.configure do |config|
  config.include DnsMock::TestFramework::RSpec::Helper
end

# Your awesome first_a_record_spec.rb

RSpec.describe FirstARecord do
  subject(:service) do
    described_class.call(
      hostname,
      dns_gateway_host: 'localhost',
      dns_gateway_port: dns_mock_server.port
    )
  end

  let(:hostname) { 'example.com' }
  let(:first_a_record) { '1.2.3.4' }
  let(:records) { { hostname => { a: [first_a_record] } } }

  before { dns_mock_server.assign_mocks(records) }

  it { is_expected.to eq(first_a_record) }
end

DnsMock::TestFramework::RSpec::Interface.start_server    # creates and runs DnsMock server instance
DnsMock::TestFramework::RSpec::Interface.stop_server!    # stops current DnsMock server instance
DnsMock::TestFramework::RSpec::Interface.reset_mocks!    # resets mocks in current DnsMock server instance
DnsMock::TestFramework::RSpec::Interface.clear_messages! # clears collected lookup messages in current DnsMock server instance
DnsMock::TestFramework::RSpec::Interface.clear_server!   # stops and clears current DnsMock server instance