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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.commons.csv.issues;
  
  import static org.junit.jupiter.api.Assertions.assertThrows;
  
  import java.io.IOException;
  import java.io.StringReader;
  
  import org.apache.commons.csv.CSVFormat;
  import org.apache.commons.csv.CSVParser;
  import org.apache.commons.csv.DuplicateHeaderMode;
  import org.junit.jupiter.api.Test;
  
  /**
   * When {@link CSVFormat#withHeader(String...)} is not null; duplicate headers
   * with empty strings should not be allowed.
   *
   * @see <a href="https://issues.apache.org/jira/browse/CSV-264">Jira Ticker</a>
   */
  public class JiraCsv264Test {
  
      private static final String CSV_STRING = "\"\",\"B\",\"\"\n" +
                                               "\"1\",\"2\",\"3\"\n" +
                                               "\"4\",\"5\",\"6\"";
  
      /**
       * A CSV file with a random gap in the middle.
       */
      private static final String CSV_STRING_GAP = "\"A\",\"B\",\"\",\"\",\"E\"\n" +
                                                   "\"1\",\"2\",\"\",\"\",\"5\"\n" +
                                                   "\"6\",\"7\",\"\",\"\",\"10\"";
  
      @Test
      public void testJiraCsv264() {
          final CSVFormat csvFormat = CSVFormat.DEFAULT
              .builder()
              .setHeader()
              .setDuplicateHeaderMode(DuplicateHeaderMode.DISALLOW)
              .setAllowMissingColumnNames(true)
              .build();
  
          try (StringReader reader = new StringReader(CSV_STRING)) {
              assertThrows(IllegalArgumentException.class, () -> csvFormat.parse(reader));
          }
      }
  
      @Test
      public void testJiraCsv264WithGapAllowEmpty() throws IOException {
          final CSVFormat csvFormat = CSVFormat.DEFAULT
              .builder()
              .setHeader()
              .setDuplicateHeaderMode(DuplicateHeaderMode.ALLOW_EMPTY)
              .setAllowMissingColumnNames(true)
              .build();
  
          try (StringReader reader = new StringReader(CSV_STRING_GAP); final CSVParser parser = csvFormat.parse(reader)) {
              // empty
          }
      }
  
      @Test
      public void testJiraCsv264WithGapDisallow() {
          final CSVFormat csvFormat = CSVFormat.DEFAULT
              .builder()
              .setHeader()
              .setDuplicateHeaderMode(DuplicateHeaderMode.DISALLOW)
              .setAllowMissingColumnNames(true)
              .build();
  
          try (StringReader reader = new StringReader(CSV_STRING_GAP)) {
              assertThrows(IllegalArgumentException.class, () -> csvFormat.parse(reader));
          }
      }
  }