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Guava testlib is a set of java classes used for more convenient unit testing - particularly to assist the tests for Guava itself.

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/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed 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 com.google.common.testing;

import com.google.common.annotations.Beta;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.logging.Handler;
import java.util.logging.LogRecord;

import javax.annotation.Nullable;

/**
 * Tests may use this to intercept messages that are logged by the code under
 * test.  Example:
 *  *   TestLogHandler handler;
 *
 *   protected void setUp() throws Exception {
 *     super.setUp();
 *     handler = new TestLogHandler();
 *     SomeClass.logger.addHandler(handler);
 *     addTearDown(new TearDown() {
 *       public void tearDown() throws Exception {
 *         SomeClass.logger.removeHandler(handler);
 *       }
 *     });
 *   }
 *
 *   public void test() {
 *     SomeClass.foo();
 *     LogRecord firstRecord = handler.getStoredLogRecords().get(0);
 *     assertEquals("some message", firstRecord.getMessage());
 *   }
 * 
 *
 * @author Kevin Bourrillion
 * @since 10.0
 */
@Beta
public class TestLogHandler extends Handler {
  /** We will keep a private list of all logged records */
  private final List list =
      Collections.synchronizedList(new ArrayList());

  /**
   * Adds the most recently logged record to our list.
   */
  @Override
  public void publish(@Nullable LogRecord record) {
    list.add(record);
  }

  @Override
  public void flush() {}

  @Override
  public void close() {}

  public void clear() {
    list.clear();
  }

  /**
   * Fetch the list of logged records
   * @return unmodifiable LogRecord list of all logged records
   */
  public List getStoredLogRecords() {
    List result = new ArrayList(list);
    return Collections.unmodifiableList(result);
  }
}