diff --git a/src/test/java/CalculationsTest.java b/src/test/java/CalculationsTest.java
index 634a972..1073c19 100644
--- a/src/test/java/CalculationsTest.java
+++ b/src/test/java/CalculationsTest.java
@@ -35,5 +35,11 @@ public class CalculationsTest {
         // Test with large number
         assertEquals(3628800, fact.calculateFactorial(10));
     }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testNegativeNumber() {
+        Calculations fact = new Calculations();
+        fact.calculateFactorial(-5); // Should throw IllegalArgumentException
+    }
 }