diff --git a/test/cvdatpjunit/CVDATPJUnitTest.java b/test/cvdatpjunit/CVDATPJUnitTest.java
index fd8bb95..e25c634 100644
--- a/test/cvdatpjunit/CVDATPJUnitTest.java
+++ b/test/cvdatpjunit/CVDATPJUnitTest.java
@@ -19,5 +19,6 @@ class CVDATPJUnitTest {
         Assertions.assertEquals("TENRANI", CVDATPJUnit.swapTwoLast("TENRAIN"));
         Assertions.assertEquals("A", CVDATPJUnit.swapTwoLast("A"));
         Assertions.assertEquals("", CVDATPJUnit.swapTwoLast(""));
+        Assertions.assertNull(CVDATPJUnit.swapTwoLast(null));
     }
 }