diff --git a/tests/src/Unit/StringFormattingTest.php b/tests/src/Unit/StringFormattingTest.php
index ecbab897e..cc6b8fa67 100644
--- a/tests/src/Unit/StringFormattingTest.php
+++ b/tests/src/Unit/StringFormattingTest.php
@@ -17,6 +17,7 @@ class StringFormattingTest extends UnitTestCase {
    * @expectedExceptionMessageRegExp /Failed to create a specification compliant string representation for '.+'\./
    */
   public function testFailureOnInvalidInput() {
+    $this->expectException(InvalidArgumentException::class);
     StringHelper::camelCase('^%!@#&');
   }