Handled tag conflict from rename tag action

module/Rest/test-api/Action/UpdateTagActionTest.php

@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ShlinkioApiTest\Shlink\Rest\Action;
+
+use GuzzleHttp\RequestOptions;
+use Shlinkio\Shlink\TestUtils\ApiTest\ApiTestCase;
+
+class UpdateTagActionTest extends ApiTestCase
+{
+    /** @test */
+    public function errorIsThrownWhenTryingToRenameTagToAnotherTagName(): void
+    {
+        $resp = $this->callApiWithKey(self::METHOD_PUT, '/tags', [RequestOptions::JSON => [
+            'oldName' => 'foo',
+            'newName' => 'bar',
+        ]]);
+        $payload = $this->getJsonResponsePayload($resp);
+
+        $this->assertEquals(self::STATUS_CONFLICT, $resp->getStatusCode());
+        $this->assertEquals('TAG_CONFLICT', $payload['error']);
+    }
+
+    /** @test */
+    public function tagIsProperlyRenamedWhenRenamingToItself(): void
+    {
+        $resp = $this->callApiWithKey(self::METHOD_PUT, '/tags', [RequestOptions::JSON => [
+            'oldName' => 'foo',
+            'newName' => 'foo',
+        ]]);
+
+        $this->assertEquals(self::STATUS_NO_CONTENT, $resp->getStatusCode());
+    }
+}