diff --git a/src/test/java/org/opensearch/agent/tools/SearchAnomalyResultsToolTests.java b/src/test/java/org/opensearch/agent/tools/SearchAnomalyResultsToolTests.java
index 69d56394..0d3cc3d8 100644
--- a/src/test/java/org/opensearch/agent/tools/SearchAnomalyResultsToolTests.java
+++ b/src/test/java/org/opensearch/agent/tools/SearchAnomalyResultsToolTests.java
@@ -6,6 +6,7 @@
 package org.opensearch.agent.tools;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.doAnswer;
@@ -64,6 +65,15 @@ public void setup() {
         nonEmptyParams = Map.of("detectorId", "foo");
     }
 
+    @Test
+    public void testRunWithInvalidAnomalyGradeParam() throws Exception {
+        Tool tool = SearchAnomalyResultsTool.Factory.getInstance().create(Collections.emptyMap());
+
+        @SuppressWarnings("unchecked")
+        ActionListener<String> listener = Mockito.mock(ActionListener.class);
+        assertThrows(NumberFormatException.class, () -> tool.run(Map.of("anomalyGradeThreshold", "foo"), listener));
+    }
+
     @Test
     public void testRunWithNoResults() throws Exception {
         Tool tool = SearchAnomalyResultsTool.Factory.getInstance().create(Collections.emptyMap());