diff --git a/tests/unit/Rules/CurrencyCodeTest.php b/tests/unit/Rules/CurrencyCodeTest.php
index 51477480..fbb2245c 100644
--- a/tests/unit/Rules/CurrencyCodeTest.php
+++ b/tests/unit/Rules/CurrencyCodeTest.php
@@ -46,6 +46,7 @@ final class CurrencyCodeTest extends RuleTestCase
         $rule = new CurrencyCode();
 
         return [
+            [$rule, ''],
             [$rule, 'BTC'],
             [$rule, 'GGP'],
             [$rule, 'USA'],