add Emailer and EmailFactory interfaces with laravel + fake impls

backend/tests/Fakes/FakeEmailFactory.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace Tests\Fakes;
+
+use App\Email\EmailFactory;
+
+class FakeEmailFactory implements EmailFactory
+{
+    public function makeConfirmationEmail(string $token): string
+    {
+        return "confirm:{$token}";
+    }
+}

backend/tests/Fakes/FakeEmailer.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace Tests\Fakes;
+
+use App\Email\Emailer;
+
+class FakeEmailer implements Emailer
+{
+    /**
+     * @var array<int, array{from: string, to: string, body: string}>
+     */
+    private array $sentEmails = [];
+
+    public function send(string $from, string $to, string $body): void
+    {
+        $this->sentEmails[] = [
+            'from' => $from,
+            'to' => $to,
+            'body' => $body,
+        ];
+    }
+
+    public function getNumberOfEmailsSent(): int
+    {
+        return count($this->sentEmails);
+    }
+
+    /**
+     * @return array<int, array{from: string, to: string, body: string}>
+     */
+    public function getSentEmails(): array
+    {
+        return $this->sentEmails;
+    }
+}