Add unit tests for IFSTIndexHandler index lifecycle

pinot-segment-local/src/test/java/org/apache/pinot/segment/local/segment/index/loader/invertedindex/IFSTIndexHandlerTest.java

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+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pinot.segment.local.segment.index.loader.invertedindex;
+
+import java.util.Map;
+import java.util.Set;
+import java.util.TreeSet;
+import org.apache.pinot.segment.spi.ColumnMetadata;
+import org.apache.pinot.segment.spi.index.FieldIndexConfigs;
+import org.apache.pinot.segment.spi.index.FstIndexConfig;
+import org.apache.pinot.segment.spi.index.StandardIndexes;
+import org.apache.pinot.segment.spi.index.metadata.SegmentMetadataImpl;
+import org.apache.pinot.segment.spi.store.SegmentDirectory;
+import org.apache.pinot.spi.config.table.TableConfig;
+import org.apache.pinot.spi.data.FieldSpec;
+import org.apache.pinot.spi.data.Schema;
+import org.testng.annotations.Test;
+
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+import static org.testng.Assert.assertFalse;
+import static org.testng.Assert.assertTrue;
+
+
+/// Unit tests for [IFSTIndexHandler].
+///
+/// IFST (case-insensitive FST) indexes share the same index lifecycle as FST indexes but
+/// use a separate index type ([StandardIndexes#ifst()]) and file extension.
+///
+/// Covers:
+/// - needUpdateIndices returns true when a column is dropped from the IFST index config
+/// - updateIndices removes the on-disk index when a column is dropped from config
+/// - needUpdateIndices returns true when a new column is added to the config
+/// - needUpdateIndices returns false when the index is already present and matches config
+/// - needUpdateIndices returns false when column metadata is absent (column not in segment)
+public class IFSTIndexHandlerTest {
+  private static final String COLUMN = "category";
+
+  @Test
+  public void testNeedUpdateReturnsTrueWhenColumnRemovedFromConfig()
+      throws Exception {
+    // Column has an IFST index on disk but the new config has no IFST index for it.
+    SegmentDirectory segmentDirectory = mockSegmentDirectory(COLUMN);
+    SegmentDirectory.Reader reader = mockReader(segmentDirectory);
+
+    IFSTIndexHandler handler = new IFSTIndexHandler(segmentDirectory, Map.of(),
+        mock(TableConfig.class), mock(Schema.class));
+
+    assertTrue(handler.needUpdateIndices(reader),
+        "Rebuild expected to remove index when column is dropped from IFST index config");
+  }
+
+  @Test
+  public void testUpdateIndicesRemovesIndexWhenColumnDroppedFromConfig()
+      throws Exception {
+    SegmentDirectory segmentDirectory = mockSegmentDirectory(COLUMN);
+    SegmentDirectory.Writer writer = mock(SegmentDirectory.Writer.class);
+    when(writer.toSegmentDirectory()).thenReturn(segmentDirectory);
+
+    IFSTIndexHandler handler = new IFSTIndexHandler(segmentDirectory, Map.of(),
+        mock(TableConfig.class), mock(Schema.class));
+    handler.updateIndices(writer);
+
+    verify(writer).removeIndex(COLUMN, StandardIndexes.ifst());
+  }
+
+  @Test
+  public void testNeedUpdateReturnsTrueWhenNewColumnAdded()
+      throws Exception {
+    // Column is in config but has no existing IFST index — metadata present.
+    SegmentMetadataImpl segmentMetadata = mock(SegmentMetadataImpl.class);
+    when(segmentMetadata.getName()).thenReturn("testSegment");
+    when(segmentMetadata.getTotalDocs()).thenReturn(1);
+    when(segmentMetadata.getAllColumns()).thenReturn(new TreeSet<>(Set.of(COLUMN)));
+    ColumnMetadata columnMetadata = mock(ColumnMetadata.class);
+    when(columnMetadata.getColumnName()).thenReturn(COLUMN);
+    when(columnMetadata.getDataType()).thenReturn(FieldSpec.DataType.STRING);
+    when(columnMetadata.hasDictionary()).thenReturn(true);
+    when(columnMetadata.isSingleValue()).thenReturn(true);
+    when(segmentMetadata.getColumnMetadataFor(COLUMN)).thenReturn(columnMetadata);
+
+    SegmentDirectory segmentDirectory = mock(SegmentDirectory.class);
+    when(segmentDirectory.getSegmentMetadata()).thenReturn(segmentMetadata);
+    when(segmentDirectory.getColumnsWithIndex(StandardIndexes.ifst())).thenReturn(Set.of());
+
+    SegmentDirectory.Reader reader = mock(SegmentDirectory.Reader.class);
+    when(reader.toSegmentDirectory()).thenReturn(segmentDirectory);
+
+    assertTrue(createHandler(segmentDirectory).needUpdateIndices(reader),
+        "New IFST index expected for column added to config with metadata present");
+  }
+
+  @Test
+  public void testNeedUpdateReturnsFalseWhenColumnMetadataAbsent()
+      throws Exception {
+    // Column is in config but getColumnMetadataFor returns null — not yet in segment.
+    SegmentMetadataImpl segmentMetadata = mock(SegmentMetadataImpl.class);
+    when(segmentMetadata.getName()).thenReturn("testSegment");
+    when(segmentMetadata.getTotalDocs()).thenReturn(1);
+    when(segmentMetadata.getAllColumns()).thenReturn(new TreeSet<>(Set.of(COLUMN)));
+    when(segmentMetadata.getColumnMetadataFor(COLUMN)).thenReturn(null);
+
+    SegmentDirectory segmentDirectory = mock(SegmentDirectory.class);
+    when(segmentDirectory.getSegmentMetadata()).thenReturn(segmentMetadata);
+    when(segmentDirectory.getColumnsWithIndex(StandardIndexes.ifst())).thenReturn(Set.of());
+
+    SegmentDirectory.Reader reader = mock(SegmentDirectory.Reader.class);
+    when(reader.toSegmentDirectory()).thenReturn(segmentDirectory);
+
+    assertFalse(createHandler(segmentDirectory).needUpdateIndices(reader),
+        "No update expected when column metadata is absent");
+  }
+
+  @Test
+  public void testNeedUpdateReturnsFalseWhenIndexUpToDate()
+      throws Exception {
+    // Column has an IFST index and is still in config — nothing to do.
+    SegmentDirectory segmentDirectory = mockSegmentDirectory(COLUMN);
+    SegmentDirectory.Reader reader = mockReader(segmentDirectory);
+
+    assertFalse(createHandler(segmentDirectory).needUpdateIndices(reader),
+        "No update expected when IFST index is present and matches config");
+  }
+
+  private static IFSTIndexHandler createHandler(SegmentDirectory segmentDirectory) {
+    FieldIndexConfigs fieldIndexConfigs =
+        new FieldIndexConfigs.Builder().add(StandardIndexes.ifst(), new FstIndexConfig()).build();
+    return new IFSTIndexHandler(segmentDirectory, Map.of(COLUMN, fieldIndexConfigs),
+        mock(TableConfig.class), mock(Schema.class));
+  }
+
+  private static SegmentDirectory mockSegmentDirectory(String column) {
+    SegmentMetadataImpl segmentMetadata = mock(SegmentMetadataImpl.class);
+    when(segmentMetadata.getName()).thenReturn("testSegment");
+    when(segmentMetadata.getTotalDocs()).thenReturn(1);
+    when(segmentMetadata.getAllColumns()).thenReturn(new TreeSet<>(Set.of(column)));
+
+    SegmentDirectory segmentDirectory = mock(SegmentDirectory.class);
+    when(segmentDirectory.getSegmentMetadata()).thenReturn(segmentMetadata);
+    when(segmentDirectory.getColumnsWithIndex(StandardIndexes.ifst())).thenReturn(Set.of(column));
+    return segmentDirectory;
+  }
+
+  private static SegmentDirectory.Reader mockReader(SegmentDirectory segmentDirectory) {
+    SegmentDirectory.Reader reader = mock(SegmentDirectory.Reader.class);
+    when(reader.toSegmentDirectory()).thenReturn(segmentDirectory);
+    return reader;
+  }
+}