lucene/misc/src/test/org/apache/lucene/search/similarity/TestLegacyBM25Similarity.java

/*
 * 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.lucene.search.similarity;

import java.util.Random;

import org.apache.lucene.search.similarities.BM25Similarity;
import org.apache.lucene.search.similarities.BaseSimilarityTestCase;
import org.apache.lucene.search.similarities.Similarity;

public class TestLegacyBM25Similarity extends BaseSimilarityTestCase {

  public void testIllegalK1() {
    IllegalArgumentException expected = expectThrows(IllegalArgumentException.class, () -> {
      new LegacyBM25Similarity(Float.POSITIVE_INFINITY, 0.75f);
    });
    assertTrue(expected.getMessage().contains("illegal k1 value"));

    expected = expectThrows(IllegalArgumentException.class, () -> {
      new LegacyBM25Similarity(-1, 0.75f);
    });
    assertTrue(expected.getMessage().contains("illegal k1 value"));

    expected = expectThrows(IllegalArgumentException.class, () -> {
      new LegacyBM25Similarity(Float.NaN, 0.75f);
    });
    assertTrue(expected.getMessage().contains("illegal k1 value"));
  }

  public void testIllegalB() {
    IllegalArgumentException expected = expectThrows(IllegalArgumentException.class, () -> {
      new LegacyBM25Similarity(1.2f, 2f);
    });
    assertTrue(expected.getMessage().contains("illegal b value"));

    expected = expectThrows(IllegalArgumentException.class, () -> {
      new LegacyBM25Similarity(1.2f, -1f);
    });
    assertTrue(expected.getMessage().contains("illegal b value"));

    expected = expectThrows(IllegalArgumentException.class, () -> {
      new LegacyBM25Similarity(1.2f, Float.POSITIVE_INFINITY);
    });
    assertTrue(expected.getMessage().contains("illegal b value"));

    expected = expectThrows(IllegalArgumentException.class, () -> {
      new LegacyBM25Similarity(1.2f, Float.NaN);
    });
    assertTrue(expected.getMessage().contains("illegal b value"));
  }

  public void testDefaults() {
    LegacyBM25Similarity legacyBM25Similarity = new LegacyBM25Similarity();
    BM25Similarity bm25Similarity = new BM25Similarity();
    assertEquals(bm25Similarity.getB(), legacyBM25Similarity.getB(), 0f);
    assertEquals(bm25Similarity.getK1(), legacyBM25Similarity.getK1(), 0f);
  }

  public void testToString() {
    LegacyBM25Similarity legacyBM25Similarity = new LegacyBM25Similarity();
    BM25Similarity bm25Similarity = new BM25Similarity();
    assertEquals(bm25Similarity.toString(), legacyBM25Similarity.toString());
  }

  @Override
  protected Similarity getSimilarity(Random random) {
    return new LegacyBM25Similarity(randomK1(random), randomB(random));
  }

  private static float randomK1(Random random) {
    // term frequency normalization parameter k1
    switch (random.nextInt(4)) {
      case 0:
        // minimum value
        return 0;
      case 1:
        // tiny value
        return Float.MIN_VALUE;
      case 2:
        // maximum value
        // upper bounds on individual term's score is 43.262806 * (k1 + 1) * boost
        // we just limit the test to "reasonable" k1 values but don't enforce this anywhere.
        return Integer.MAX_VALUE;
      default:
        // random value
        return Integer.MAX_VALUE * random.nextFloat();
    }
  }

  private static float randomB(Random random) {
    // length normalization parameter b [0 .. 1]
    switch (random.nextInt(4)) {
      case 0:
        // minimum value
        return 0;
      case 1:
        // tiny value
        return Float.MIN_VALUE;
      case 2:
        // maximum value
        return 1;
      default:
        // random value
        return random.nextFloat();
    }
  }
}