Ensured domain is taken into account when checking if a slug is in use

module/Core/test/Exception/NonUniqueSlugExceptionTest.php

@@ -0,0 +1,34 @@
+<?php
+declare(strict_types=1);
+
+namespace ShlinkioTest\Shlink\Core\Exception;
+
+use PHPUnit\Framework\TestCase;
+use Shlinkio\Shlink\Core\Exception\NonUniqueSlugException;
+
+class NonUniqueSlugExceptionTest extends TestCase
+{
+    /**
+     * @test
+     * @dataProvider provideMessages
+     */
+    public function properlyCreatesExceptionFromSlug(string $expectedMessage, string $slug, ?string $domain): void
+    {
+        $e = NonUniqueSlugException::fromSlug($slug, $domain);
+        $this->assertEquals($expectedMessage, $e->getMessage());
+    }
+
+    public function provideMessages(): iterable
+    {
+        yield 'without domain' => [
+            'Provided slug "foo" is not unique.',
+            'foo',
+            null,
+        ];
+        yield 'with domain' => [
+            'Provided slug "baz" is not unique for domain "bar".',
+            'baz',
+            'bar',
+        ];
+    }
+}