diff --git a/tests/classes/Factory.php b/tests/classes/Factory.php
index 0d794fc..7ac5c96 100644
--- a/tests/classes/Factory.php
+++ b/tests/classes/Factory.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 class Factory
 {
     // Cannot be instantiated
diff --git a/tests/classes/Hello.php b/tests/classes/Hello.php
index 3bf3230..f533c3a 100644
--- a/tests/classes/Hello.php
+++ b/tests/classes/Hello.php
@@ -1,13 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 class Hello
 {
-    public function sayHi()
+    public function sayHi(): string
     {
         return 'hello';
     }
 
-    public static function sayBye()
+    public static function sayBye(): string
     {
         return 'goodbye';
     }
diff --git a/tests/classes/TesterClass.php b/tests/classes/TesterClass.php
index 567ea37..662f7b2 100644
--- a/tests/classes/TesterClass.php
+++ b/tests/classes/TesterClass.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 class TesterClass
 {
     public $param1;
diff --git a/tests/classes/User.php b/tests/classes/User.php
index 4ec8cc9..fb81f00 100644
--- a/tests/classes/User.php
+++ b/tests/classes/User.php
@@ -1,10 +1,12 @@
 <?php
 
+declare(strict_types=1);
+
 class User
 {
-    public $name;
+    public string $name;
 
-    public function __construct($name = '')
+    public function __construct(string $name = '')
     {
         $this->name = $name;
     }