test EmailAddress value object

7 cases: rejects spaces, double-@, empty input; trims whitespace;
lowercases domain only (preserving local-part case); equality by
normalized value; __toString and getDomain. fails red - class
App\\Shared\\ValueObject\\EmailAddress not yet defined.

backend/tests/Unit/Shared/ValueObject/EmailAddressTest.php

@@ -0,0 +1,61 @@
+<?php
+
+namespace Tests\Unit\Shared\ValueObject;
+
+use App\Shared\ValueObject\EmailAddress;
+use InvalidArgumentException;
+use Tests\TestCase;
+
+class EmailAddressTest extends TestCase
+{
+    public function test_it_throws_on_invalid_spaces_in_email(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Invalid email address: inv alid @spa cing.co m');
+
+        new EmailAddress('inv alid @spa cing.co m');
+    }
+
+    public function test_it_throws_on_invalid_email_format(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Invalid email address: invalid-email@format@com');
+
+        new EmailAddress('invalid-email@format@com');
+    }
+
+    public function test_it_throws_on_empty_email(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Invalid email address: ');
+
+        new EmailAddress('');
+    }
+
+    public function test_it_trims_and_normalizes_domain_case(): void
+    {
+        $email = new EmailAddress(' tEsT@YaHoO.cOm ');
+        $this->assertSame('tEsT@yahoo.com', $email->value());
+    }
+
+    public function test_equality_is_by_normalized_value(): void
+    {
+        $first = new EmailAddress('test@TEST.COM');
+        $second = new EmailAddress('test@test.com');
+
+        $this->assertTrue($first->equals($second));
+        $this->assertTrue($second->equals($first));
+    }
+
+    public function test_to_string_returns_normalized_email(): void
+    {
+        $email = new EmailAddress('Test@GMAIL.COM   ');
+        $this->assertSame('Test@gmail.com', $email->__toString());
+    }
+
+    public function test_get_domain_returns_lowercased_domain(): void
+    {
+        $email = new EmailAddress('User@SubDomain.Example.COM');
+        $this->assertSame('subdomain.example.com', $email->getDomain());
+    }
+}