Added more tests for new logics

module/Core/test/Entity/ShortUrlTest.php

@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ShlinkioTest\Shlink\Core\Entity;
+
+use PHPUnit\Framework\TestCase;
+use Shlinkio\Shlink\Core\Entity\ShortUrl;
+use Shlinkio\Shlink\Core\Exception\ShortCodeCannotBeRegeneratedException;
+use Shlinkio\Shlink\Core\Model\ShortUrlMeta;
+
+class ShortUrlTest extends TestCase
+{
+    /**
+     * @test
+     * @dataProvider provideInvalidShortUrls
+     */
+    public function regenerateShortCodeThrowsExceptionIfStateIsInvalid(
+        ShortUrl $shortUrl,
+        string $expectedMessage
+    ): void {
+        $this->expectException(ShortCodeCannotBeRegeneratedException::class);
+        $this->expectExceptionMessage($expectedMessage);
+
+        $shortUrl->regenerateShortCode();
+    }
+
+    public function provideInvalidShortUrls(): iterable
+    {
+        yield 'with custom slug' => [
+            new ShortUrl('', ShortUrlMeta::createFromRawData(['customSlug' => 'custom-slug'])),
+            'The short code cannot be regenerated on ShortUrls where a custom slug was provided.',
+        ];
+        yield 'already persisted' => [
+            (new ShortUrl(''))->setId('1'),
+            'The short code can be regenerated only on new ShortUrls which have not been persisted yet.',
+        ];
+    }
+
+    /** @test */
+    public function regenerateShortCodeProperlyChangesTheValueOnValidShortUrls(): void
+    {
+        $shortUrl = new ShortUrl('');
+        $firstShortCode = $shortUrl->getShortCode();
+
+        $shortUrl->regenerateShortCode();
+        $secondShortCode = $shortUrl->getShortCode();
+
+        $this->assertNotEquals($firstShortCode, $secondShortCode);
+    }
+}