refactor: refactor the SMTP sender

spec/lib/smtp_client/server_spec.rb

@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+module SMTPClient
+
+  RSpec.describe Server do
+    let(:hostname) { "example.com" }
+    let(:port) { 25 }
+    let(:ssl_mode) { SSLModes::AUTO }
+
+    subject(:server) { described_class.new(hostname, port: port, ssl_mode: ssl_mode) }
+
+    describe "#endpoints" do
+      context "when there are A and AAAA records" do
+        before do
+          allow(DNSResolver.local).to receive(:a).and_return(["1.2.3.4", "2.3.4.5"])
+          allow(DNSResolver.local).to receive(:aaaa).and_return(["2a00::67a0:a::1234", "2a00::67a0:a::2345"])
+        end
+
+        it "asks the resolver for the A and AAAA records for the hostname" do
+          server.endpoints
+          expect(DNSResolver.local).to have_received(:a).with(hostname).once
+          expect(DNSResolver.local).to have_received(:aaaa).with(hostname).once
+        end
+
+        it "returns endpoints for ipv6 addresses followed by ipv4" do
+          expect(server.endpoints).to match [
+            have_attributes(ip_address: "2a00::67a0:a::1234"),
+            have_attributes(ip_address: "2a00::67a0:a::2345"),
+            have_attributes(ip_address: "1.2.3.4"),
+            have_attributes(ip_address: "2.3.4.5")
+          ]
+        end
+      end
+
+      context "when there are just A records" do
+        before do
+          allow(DNSResolver.local).to receive(:a).and_return(["1.2.3.4", "2.3.4.5"])
+          allow(DNSResolver.local).to receive(:aaaa).and_return([])
+        end
+
+        it "returns ipv4 endpoints" do
+          expect(server.endpoints).to match [
+            have_attributes(ip_address: "1.2.3.4"),
+            have_attributes(ip_address: "2.3.4.5")
+          ]
+        end
+      end
+
+      context "when there are just AAAA records" do
+        before do
+          allow(DNSResolver.local).to receive(:a).and_return([])
+          allow(DNSResolver.local).to receive(:aaaa).and_return(["2a00::67a0:a::1234", "2a00::67a0:a::2345"])
+        end
+
+        it "returns ipv6 endpoints" do
+          expect(server.endpoints).to match [
+            have_attributes(ip_address: "2a00::67a0:a::1234"),
+            have_attributes(ip_address: "2a00::67a0:a::2345")
+          ]
+        end
+      end
+    end
+  end
+
+end