lucene/core/src/test/org/apache/lucene/util/automaton/TestDeterminism.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,
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package org.apache.lucene.util.automaton;

import static org.apache.lucene.util.automaton.Operations.DEFAULT_MAX_DETERMINIZED_STATES;

import org.apache.lucene.util.LuceneTestCase;

/** Not completely thorough, but tries to test determinism correctness somewhat randomly. */
public class TestDeterminism extends LuceneTestCase {

  /** test a bunch of random regular expressions */
  public void testRegexps() throws Exception {
    int num = atLeast(500);
    for (int i = 0; i < num; i++) {
      assertAutomaton(
          new RegExp(AutomatonTestUtil.randomRegexp(random()), RegExp.NONE).toAutomaton());
    }
  }

  /** test against a simple, unoptimized det */
  public void testAgainstSimple() throws Exception {
    int num = atLeast(200);
    for (int i = 0; i < num; i++) {
      Automaton a = AutomatonTestUtil.randomAutomaton(random());
      a = AutomatonTestUtil.determinizeSimple(a);
      Automaton b = Operations.determinize(a, Integer.MAX_VALUE);
      // TODO: more verifications possible?
      assertTrue(Operations.sameLanguage(a, b));
    }
  }

  private static void assertAutomaton(Automaton a) {
    a = Operations.determinize(Operations.removeDeadStates(a), DEFAULT_MAX_DETERMINIZED_STATES);

    // complement(complement(a)) = a
    Automaton equivalent =
        Operations.complement(
            Operations.complement(a, DEFAULT_MAX_DETERMINIZED_STATES),
            DEFAULT_MAX_DETERMINIZED_STATES);
    assertTrue(Operations.sameLanguage(a, equivalent));

    // a union a = a
    equivalent =
        Operations.determinize(
            Operations.removeDeadStates(Operations.union(a, a)), DEFAULT_MAX_DETERMINIZED_STATES);
    assertTrue(Operations.sameLanguage(a, equivalent));

    // a intersect a = a
    equivalent =
        Operations.determinize(
            Operations.removeDeadStates(Operations.intersection(a, a)),
            DEFAULT_MAX_DETERMINIZED_STATES);
    assertTrue(Operations.sameLanguage(a, equivalent));

    // a minus a = empty
    Automaton empty = Operations.minus(a, a, DEFAULT_MAX_DETERMINIZED_STATES);
    assertTrue(Operations.isEmpty(empty));

    // as long as don't accept the empty string
    // then optional(a) - empty = a
    if (!Operations.run(a, "")) {
      // System.out.println("test " + a);
      Automaton optional = Operations.optional(a);
      // System.out.println("optional " + optional);
      equivalent =
          Operations.minus(optional, Automata.makeEmptyString(), DEFAULT_MAX_DETERMINIZED_STATES);
      // System.out.println("equiv " + equivalent);
      assertTrue(Operations.sameLanguage(a, equivalent));
    }
  }
}