diff --git a/build.gradle b/build.gradle
index 43f2a4101..c37888655 100644
--- a/build.gradle
+++ b/build.gradle
@@ -576,9 +576,6 @@ List<String> jacocoExclusions = [
         // https://github.com/opensearch-project/anomaly-detection/issues/241
         'org.opensearch.ad.task.ADBatchTaskRunner',
         'org.opensearch.ad.task.ADTaskManager',
-
-        //TODO: custom result index caused coverage drop
-        'org.opensearch.ad.transport.handler.AnomalyResultBulkIndexHandler'
 ]
 
 
diff --git a/src/test/java/org/opensearch/ad/transport/handler/AnomalyResultBulkIndexHandlerTests.java b/src/test/java/org/opensearch/ad/transport/handler/AnomalyResultBulkIndexHandlerTests.java
index a6959b260..1ee99af7d 100644
--- a/src/test/java/org/opensearch/ad/transport/handler/AnomalyResultBulkIndexHandlerTests.java
+++ b/src/test/java/org/opensearch/ad/transport/handler/AnomalyResultBulkIndexHandlerTests.java
@@ -19,6 +19,7 @@
 import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
 import static org.opensearch.ad.constant.CommonName.ANOMALY_RESULT_INDEX_ALIAS;
 
 import java.io.IOException;
@@ -94,6 +95,39 @@ public void testNullAnomalyResults() {
         verify(anomalyDetectionIndices, never()).doesAnomalyDetectorIndexExist();
     }
 
+    public void testAnomalyResultBulkIndexHandler_IndexNotExist() {
+        when(anomalyDetectionIndices.doesIndexExist("testIndex")).thenReturn(false);
+        AnomalyResult anomalyResult = mock(AnomalyResult.class);
+        when(anomalyResult.getDetectorId()).thenReturn("testId");
+
+        bulkIndexHandler.bulkIndexAnomalyResult("testIndex", ImmutableList.of(anomalyResult), listener);
+        verify(listener, times(1)).onFailure(exceptionCaptor.capture());
+        assertEquals("Can't find result index testIndex", exceptionCaptor.getValue().getMessage());
+    }
+
+    public void testAnomalyResultBulkIndexHandler_InValidResultIndexMapping() {
+        when(anomalyDetectionIndices.doesIndexExist("testIndex")).thenReturn(true);
+        when(anomalyDetectionIndices.isValidResultIndexMapping("testIndex")).thenReturn(false);
+        AnomalyResult anomalyResult = mock(AnomalyResult.class);
+        when(anomalyResult.getDetectorId()).thenReturn("testId");
+
+        bulkIndexHandler.bulkIndexAnomalyResult("testIndex", ImmutableList.of(anomalyResult), listener);
+        verify(listener, times(1)).onFailure(exceptionCaptor.capture());
+        assertEquals("wrong index mapping of custom AD result index", exceptionCaptor.getValue().getMessage());
+    }
+
+    public void testAnomalyResultBulkIndexHandler_FailBulkIndexAnomaly() throws IOException {
+        when(anomalyDetectionIndices.doesIndexExist("testIndex")).thenReturn(true);
+        when(anomalyDetectionIndices.isValidResultIndexMapping("testIndex")).thenReturn(true);
+        AnomalyResult anomalyResult = mock(AnomalyResult.class);
+        when(anomalyResult.getDetectorId()).thenReturn("testId");
+        when(anomalyResult.toXContent(any(), any())).thenThrow(new RuntimeException());
+
+        bulkIndexHandler.bulkIndexAnomalyResult("testIndex", ImmutableList.of(anomalyResult), listener);
+        verify(listener, times(1)).onFailure(exceptionCaptor.capture());
+        assertEquals("Failed to prepare request to bulk index anomaly results", exceptionCaptor.getValue().getMessage());
+    }
+
     public void testCreateADResultIndexNotAcknowledged() throws IOException {
         doAnswer(invocation -> {
             ActionListener<CreateIndexResponse> listener = invocation.getArgument(0);