Test Appender

TestAppender.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 com.cloud.test.util;

import com.google.common.base.Joiner;
import com.google.common.base.Objects;
import com.google.common.collect.ImmutableMap;
import org.apache.log4j.AppenderSkeleton;
import org.apache.log4j.Level;
import org.apache.log4j.Logger;
import org.apache.log4j.spi.LoggingEvent;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.regex.Pattern;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.base.Strings.isNullOrEmpty;
import static java.lang.String.format;
import static org.apache.log4j.Level.ALL;
import static org.apache.log4j.Level.DEBUG;
import static org.apache.log4j.Level.ERROR;
import static org.apache.log4j.Level.FATAL;
import static org.apache.log4j.Level.INFO;
import static org.apache.log4j.Level.OFF;
import static org.junit.Assert.fail;

/**
 *
 * Tracks one or more patterns to determine whether or not they have been
 * logged.  It uses a streaming approach to determine whether or not a message
 * has a occurred to prevent unnecessary memory consumption.  Instances of this
 * of this class are created using the {@link TestAppenderBuilder}.
 *
 * To use this class, register a one or more expected patterns by level as part
 * of the test setup and retain an reference to the appender instance.  After the
 * expected logging events have occurred in the test case, call
 * {@link TestAppender#assertMessagesLogged()} which will fail the test if any of the
 * expected patterns were not logged.
 *
 */
public final class TestAppender extends AppenderSkeleton {

    private final static String APPENDER_NAME = "test_appender";

    private final ImmutableMap<Level, Set<PatternResult>> expectedPatternResults;

    private TestAppender(final Map<Level, Set<PatternResult>> expectedPatterns) {

        super();

        expectedPatternResults = ImmutableMap.copyOf(expectedPatterns);

    }

    protected void append(LoggingEvent loggingEvent) {

        checkArgument(loggingEvent != null, "append requires a non-null loggingEvent");

        final Level level = loggingEvent.getLevel();

        checkState(expectedPatternResults.containsKey(level), "level " + level + " not supported by append");

        for (final PatternResult patternResult : expectedPatternResults.get(level)) {

            if (patternResult.getPattern().matcher(loggingEvent.getRenderedMessage()).matches()) {
                patternResult.markFound();
            }

        }

    }

    public void close() {
        // Do nothing ...
    }

    public boolean requiresLayout() {
        return false;
    }

    public void assertMessagesLogged() {

        final List<String> unloggedPatterns = new ArrayList<>();

        for (final Map.Entry<Level, Set<PatternResult>> expectedPatternResult : expectedPatternResults.entrySet()) {

            for (final PatternResult patternResults : expectedPatternResult.getValue()) {
                if (!patternResults.isFound()) {
                    unloggedPatterns.add(format("%1$s was not logged for level %2$s",
                            patternResults.getPattern().toString(), expectedPatternResult.getKey()));
                }
            }

        }

        if (!unloggedPatterns.isEmpty()) {
            fail(Joiner.on(",").join(unloggedPatterns));
        }

    }

    private static final class PatternResult {

        private final Pattern pattern;
        private boolean foundFlag = false;

        private PatternResult(Pattern pattern) {

            super();

            this.pattern = pattern;

        }

        public Pattern getPattern() {
            return pattern;
        }

        public void markFound() {
            // This operation is thread-safe because the value will only ever be switched from false to true.  Therefore,
            // multiple threads mutating the value for a pattern will not corrupt the value ...
            foundFlag = true;
        }

        public boolean isFound() {
            return foundFlag;
        }

        @Override
        public boolean equals(Object thatObject) {
            if (this == thatObject) {
                return true;
            }

            if (thatObject == null || getClass() != thatObject.getClass()) {
                return false;
            }

            PatternResult thatPatternResult = (PatternResult) thatObject;

            return foundFlag == thatPatternResult.foundFlag &&
                    Objects.equal(pattern, thatPatternResult.pattern);
        }

        @Override
        public int hashCode() {
            return Objects.hashCode(pattern, foundFlag);
        }

        @Override
        public String toString() {
            return format("Pattern Result [ pattern: %1$s, markFound: %2$s ]", pattern.toString(), foundFlag);
        }

    }

    public static final class TestAppenderBuilder {

        private final Map<Level, Set<PatternResult>> expectedPatterns;

        public TestAppenderBuilder() {

            super();

            expectedPatterns = new HashMap<>();

            expectedPatterns.put(ALL, new HashSet<PatternResult>());
            expectedPatterns.put(DEBUG, new HashSet<PatternResult>());
            expectedPatterns.put(ERROR, new HashSet<PatternResult>());
            expectedPatterns.put(FATAL, new HashSet<PatternResult>());
            expectedPatterns.put(INFO, new HashSet<PatternResult>());
            expectedPatterns.put(OFF, new HashSet<PatternResult>());

        }

        public TestAppenderBuilder addExpectedPattern(final Level level, final String pattern) {

            checkArgument(level != null, "addExpectedPattern requires a non-null level");
            checkArgument(isNullOrEmpty(pattern), "addExpectedPattern requires a non-blank pattern");
            checkState(expectedPatterns.containsKey(level), "level " + level + " is not supported by " + getClass().getName());

            expectedPatterns.get(level).add(new PatternResult(Pattern.compile(pattern)));

            return this;

        }

        public TestAppender build() {
            return new TestAppender(expectedPatterns);
        }

    }

    /**
     *
     * Attaches a {@link TestAppender} to a {@link Logger} and ensures that it is the only
     * test appender attached to the logger.
     *
     * @param logger The logger which will be monitored by the test
     * @param testAppender The test appender to attach to {@code logger}
     */
    public static void safeAddAppender(Logger logger, TestAppender testAppender) {
        logger.removeAppender(APPENDER_NAME);
        logger.addAppender(testAppender);
    }

}