Added more tests

Author: danitome24

tests/User/PasswordTest.php

@@ -38,4 +38,10 @@ public function passwords()
             [Password::build('somepwd'), Password::build('somepwddif'), false]
         ];
     }
+
+    public function testToStringMagicMethod()
+    {
+        $pwd = Password::build('securestpwd');
+        $this->assertEquals('securestpwd', $pwd);
+    }
 }

tests/User/UsernameTest.php

@@ -46,4 +46,10 @@ public function usernames()
             [Username::fromString('dfernandez'), Username::fromString('tests'), false]
         ];
     }
+
+    public function testToStringMagicMethod()
+    {
+        $username = Username::fromString('username');
+        $this->assertEquals('username', $username);
+    }
 }