Fix deprecation warnings

Author: Art4

phpunit.xml

@@ -1,16 +1,16 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         backupGlobals="false"
-         colors="true"
-         processIsolation="false"
-         stopOnFailure="false"
-         stopOnError="false"
-         stopOnIncomplete="false"
-         stopOnSkipped="false"
-         bootstrap="vendor/autoload.php"
          xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.4/phpunit.xsd"
+         bootstrap="vendor/autoload.php"
          cacheDirectory=".phpunit.cache"
-         backupStaticProperties="false"
+         colors="true"
+         beStrictAboutOutputDuringTests="true"
+         displayDetailsOnIncompleteTests="true"
+         displayDetailsOnSkippedTests="true"
+         displayDetailsOnTestsThatTriggerDeprecations="true"
+         displayDetailsOnTestsThatTriggerErrors="true"
+         displayDetailsOnTestsThatTriggerNotices="true"
+         displayDetailsOnTestsThatTriggerWarnings="true"
 >
   <coverage/>
   <testsuites>

tests/Unit/V1/RelationshipLinkTest.php

@@ -31,6 +31,8 @@ class RelationshipLinkTest extends TestCase
 {
     use HelperTrait;
 
+    private Accessable $relationship;
+
     /**
      * @setup
      */