Fix null indexFieldMap bug & add UTs

src/main/java/org/opensearch/plugin/insights/core/service/categorizer/IndicesFieldTypeCache.java

@@ -68,9 +68,11 @@ IndexFieldMap getOrInitialize(Index index) {
 
     public void invalidate(Index index) {
         IndexFieldMap indexFieldMap = cache.get(index);
-        evictionCount.inc(indexFieldMap.fieldTypeMap.size());
-        entryCount.dec(indexFieldMap.fieldTypeMap.size());
-        weight.dec(indexFieldMap.weight());
+        if (indexFieldMap != null) {
+            evictionCount.inc(indexFieldMap.fieldTypeMap.size());
+            entryCount.dec(indexFieldMap.fieldTypeMap.size());
+            weight.dec(indexFieldMap.weight());
+        }
         cache.invalidate(index);
     }
 

src/test/java/org/opensearch/plugin/insights/core/service/categorizer/IndicesFieldTypeCacheTests.java

@@ -0,0 +1,64 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.plugin.insights.core.service.categorizer;
+
+import java.util.UUID;
+import java.util.stream.StreamSupport;
+import org.opensearch.common.settings.Settings;
+import org.opensearch.core.index.Index;
+import org.opensearch.test.OpenSearchTestCase;
+
+public final class IndicesFieldTypeCacheTests extends OpenSearchTestCase {
+    final Index index1 = new Index("index1", UUID.randomUUID().toString());
+    final Index index2 = new Index("index2", UUID.randomUUID().toString());
+
+    public IndicesFieldTypeCacheTests() {}
+
+    public void testCache() {
+        final IndicesFieldTypeCache indicesFieldTypeCache = new IndicesFieldTypeCache(Settings.EMPTY);
+
+        // Assert cache is empty
+        assertEquals(0, StreamSupport.stream(indicesFieldTypeCache.keySet().spliterator(), false).count());
+        assertEquals(0, (long) indicesFieldTypeCache.getEntryCount());
+        assertEquals(0, (long) indicesFieldTypeCache.getEvictionCount());
+        assertEquals(0, (long) indicesFieldTypeCache.getWeight());
+
+        // Test invalidate on empty cache
+        indicesFieldTypeCache.invalidate(index1);
+        indicesFieldTypeCache.invalidate(index2);
+
+        // Insert some items in the cache
+        if (indicesFieldTypeCache.getOrInitialize(index1).putIfAbsent("field1", "keyword")) {
+            indicesFieldTypeCache.incrementCountAndWeight("field1", "keyword");
+        }
+        if (indicesFieldTypeCache.getOrInitialize(index1).putIfAbsent("field2", "boolean")) {
+            indicesFieldTypeCache.incrementCountAndWeight("field2", "boolean");
+        }
+        if (indicesFieldTypeCache.getOrInitialize(index2).putIfAbsent("field3", "float_range")) {
+            indicesFieldTypeCache.incrementCountAndWeight("field3", "float_range");
+        }
+        if (indicesFieldTypeCache.getOrInitialize(index2).putIfAbsent("field4", "date")) {
+            indicesFieldTypeCache.incrementCountAndWeight("field4", "date");
+        }
+
+        assertEquals(2, StreamSupport.stream(indicesFieldTypeCache.keySet().spliterator(), false).count());
+        assertEquals(4, (long) indicesFieldTypeCache.getEntryCount());
+        assertEquals(0, (long) indicesFieldTypeCache.getEvictionCount());
+        assertTrue(0 < indicesFieldTypeCache.getWeight());
+
+        // Invalidate index1
+        indicesFieldTypeCache.invalidate(index1);
+
+        assertEquals(1, StreamSupport.stream(indicesFieldTypeCache.keySet().spliterator(), false).count());
+        assertEquals(2, (long) indicesFieldTypeCache.getEntryCount());
+        assertEquals(2, (long) indicesFieldTypeCache.getEvictionCount());
+        assertTrue(0 < indicesFieldTypeCache.getWeight());
+    }
+
+}