README.md in truemail-3.0.0 vs README.md in truemail-3.0.1

@@ -1449,9 +1449,59 @@
     config.blacklisted_domains = Constants::Email::BLACK_DOMAINS
   end
 end
 ```
 
+Or you can use end-to-end approach and mock DNS and SMTP services with [`dns_mock`](https://github.com/mocktools/ruby-dns-mock), [`smtp_mock`](https://github.com/mocktools/ruby-smtp-mock) for your test environment like in example below:
+
+```ruby
+# Gemfile
+
+group :test do
+  gem 'dns_mock', require: false
+  gem 'smtp_mock', require: false
+end
+
+# spec/spec_helper.rb
+
+require 'dns_mock/test_framework/rspec'
+require 'smtp_mock/test_framework/rspec'
+
+RSpec.configure do |config|
+  config.include DnsMock::TestFramework::RSpec::Helper
+  config.include SmtpMock::TestFramework::RSpec::Helper
+end
+
+# spec/integration_spec.rb
+
+RSpec.describe 'integration tests' do
+  let(:target_email) { random_email }
+  let(:dns_mock_records) { dns_mock_records_by_email(target_email, dimension: 2) }
+
+  before do
+    dns_mock_server.assign_mocks(dns_mock_records)
+    smtp_mock_server(**smtp_mock_server_options)
+
+    Truemail.configuration.tap do |config|
+      config.dns = %W[127.0.0.1:#{dns_mock_server.port}]
+      config.smtp_port = smtp_mock_server.port
+    end
+  end
+
+  context 'when checks real email' do
+    let(:smtp_mock_server_options) { {} }
+
+    it { expect(Truemail.validate(target_email).result).to be_valid }
+  end
+
+  context 'when checks fake email' do
+    let(:smtp_mock_server_options) { { not_registered_emails: [target_email] } }
+
+    it { expect(Truemail.validate(target_email).result).not_to be_valid }
+  end
+end
+```
+
 ---
 
 ## Truemail family
 
 All Truemail solutions: https://truemail-rb.org