Add LogRecorder utility (#897)

Co-authored-by: strangelookingnerd <[email protected]>
Co-authored-by: Tim Jacomb <[email protected]>

src/main/java/org/jvnet/hudson/test/LogRecorder.java

@@ -0,0 +1,335 @@
+/*
+ * The MIT License
+ *
+ * Copyright 2025 Jenkins project contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package org.jvnet.hudson.test;
+
+import edu.umd.cs.findbugs.annotations.CheckForNull;
+import edu.umd.cs.findbugs.annotations.NonNull;
+import hudson.util.RingBufferLogHandler;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.logging.ConsoleHandler;
+import java.util.logging.Formatter;
+import java.util.logging.Handler;
+import java.util.logging.Level;
+import java.util.logging.LogRecord;
+import java.util.logging.Logger;
+import java.util.logging.SimpleFormatter;
+import java.util.stream.Collectors;
+import org.hamcrest.Description;
+import org.hamcrest.Matcher;
+import org.hamcrest.TypeSafeMatcher;
+
+/**
+ * A test utility which allows you to easily enable one or more loggers for the duration of a test.
+ * Call {@link #record(Class, Level)} or another overload for the recording to take effect.
+ * <p>
+ * By default, messages are merely printed to test output.
+ * If you also want to examine them, call {@link #capture}.
+ * <p>
+ * See the following example:
+ * <pre><code>
+ * try (LogRecorder recorder = new LogRecorder().record("Foo", Level.INFO).capture(100)) {
+ *     LOGGER.log(Level.INFO, "Log Message");
+ *     assertThat(recorder, LogRecorder.recorded(equalTo("Log Message")));
+ * }
+ * </code></pre>
+ */
+public class LogRecorder implements AutoCloseable {
+
+    private final Handler consoleHandler = new ConsoleHandlerWithMaxLevel();
+    private final Map<Logger, Level> loggers = new HashMap<>();
+    // initialized if and only if capture is called:
+    private RingBufferLogHandler ringHandler;
+    private List<String> messages;
+    private boolean verbose = true;
+
+    /**
+     * Initializes the recorder, by default not recording anything.
+     */
+    public LogRecorder() {
+        consoleHandler.setFormatter(new DeltaSupportLogFormatter());
+        consoleHandler.setLevel(Level.ALL);
+    }
+
+    /**
+     * Don't emit logs to the console, only record.
+     */
+    public LogRecorder quiet() {
+        this.verbose = false;
+        return this;
+    }
+
+    @Override
+    public String toString() {
+        return getRecords().stream()
+                .map(logRecord -> logRecord.getLevel().toString() + "->" + logRecord.getMessage())
+                .collect(Collectors.joining(","));
+    }
+
+    /**
+     * Initializes log record capture, in addition to merely printing it.
+     * This allows you to call {@link #getRecords} and/or {@link #getMessages} later.
+     * @param maximum the maximum number of records to keep (any further will be discarded)
+     * @return this recorder, for convenience
+     */
+    public LogRecorder capture(int maximum) {
+        messages = new ArrayList<>();
+        ringHandler = new RingBufferLogHandler(maximum) {
+            final Formatter f =
+                    new SimpleFormatter(); // placeholder instance for what should have been a static method perhaps
+
+            @Override
+            public synchronized void publish(LogRecord record) {
+                super.publish(record);
+                String message = f.formatMessage(record);
+                Throwable x = record.getThrown();
+                synchronized (messages) {
+                    messages.add(message == null && x != null ? x.toString() : message);
+                }
+            }
+        };
+        ringHandler.setLevel(Level.ALL);
+        for (Logger logger : loggers.keySet()) {
+            logger.addHandler(ringHandler);
+        }
+        return this;
+    }
+
+    /**
+     * Start listening to a logger.
+     * @param logger some logger
+     * @param level something between {@link Level#CONFIG} and {@link Level#ALL};
+     *              using {@link Level#INFO} or above is typically senseless,
+     *              since Java will by default log everything at such levels anyway;
+     *              unless you wish to inspect visible {@link #getRecords},
+     *              or wish to <em>suppress</em> console log output for some logger
+     * @return this recorder, for convenience
+     */
+    public LogRecorder record(Logger logger, Level level) {
+        loggers.put(logger, logger.getLevel());
+        logger.setLevel(level);
+        if (verbose) {
+            logger.addHandler(consoleHandler);
+        }
+        if (ringHandler != null) {
+            logger.addHandler(ringHandler);
+        }
+        return this;
+    }
+
+    /**
+     * Same as {@link #record(Logger, Level)} but calls {@link Logger#getLogger(String)} for you first.
+     */
+    public LogRecorder record(String name, Level level) {
+        return record(Logger.getLogger(name), level);
+    }
+
+    /**
+     * Same as {@link #record(String, Level)} but calls {@link Class#getName()} for you first.
+     */
+    public LogRecorder record(Class<?> clazz, Level level) {
+        return record(clazz.getName(), level);
+    }
+
+    /**
+     * Same as {@link #record(String, Level)} but calls {@link Class#getPackage()} and getName() for you first.
+     */
+    public LogRecorder recordPackage(Class<?> clazz, Level level) {
+        return record(clazz.getPackage().getName(), level);
+    }
+
+    Map<String, Level> getRecordedLevels() {
+        return loggers.keySet().stream().collect(Collectors.toMap(Logger::getName, Logger::getLevel));
+    }
+
+    /**
+     * Obtains all log records collected so far during this test case.
+     * You must have first called {@link #capture}.
+     * If more than the maximum number of records were captured, older ones will have been discarded.
+     */
+    public List<LogRecord> getRecords() {
+        return ringHandler.getView();
+    }
+
+    /**
+     * Returns a read-only view of current messages.
+     *
+     * {@link Formatter#formatMessage} applied to {@link #getRecords} at the time of logging.
+     * However, if the message is null, but there is an exception, {@link Throwable#toString} will be used.
+     * Does not include logger names, stack traces, times, etc. (these will appear in the test console anyway).
+     */
+    public List<String> getMessages() {
+        synchronized (messages) {
+            return List.copyOf(messages);
+        }
+    }
+
+    @Override
+    public void close() {
+        for (Map.Entry<Logger, Level> entry : loggers.entrySet()) {
+            Logger logger = entry.getKey();
+            logger.setLevel(entry.getValue());
+            if (verbose) {
+                logger.removeHandler(consoleHandler);
+            }
+            if (ringHandler != null) {
+                logger.removeHandler(ringHandler);
+            }
+        }
+        loggers.clear();
+        if (ringHandler != null) {
+            ringHandler.clear();
+            messages.clear();
+        }
+    }
+
+    /**
+     * Creates a {@link Matcher} that matches if the {@link LogRecorder} has a {@link LogRecord} at
+     * the specified {@link Level}, with a message matching the specified matcher, and with a
+     * {@link Throwable} matching the specified matcher.
+     * You must have first called {@link #capture}.
+     *
+     * @param level The {@link Level} of the {@link LogRecorder} to match. Pass {@code null} to match any {@link Level}.
+     * @param message the matcher to match against {@link LogRecord#getMessage}
+     * @param thrown the matcher to match against {@link LogRecord#getThrown()}. Passing {@code null} is equivalent to
+     * passing {@link org.hamcrest.Matchers#anything}
+     */
+    public static Matcher<LogRecorder> recorded(
+            @CheckForNull Level level, @NonNull Matcher<String> message, @CheckForNull Matcher<Throwable> thrown) {
+        return new RecordedMatcher(level, message, thrown);
+    }
+
+    /**
+     * Creates a {@link Matcher} that matches if the {@link LogRecorder} has a {@link LogRecord} at
+     * the specified {@link Level} and with a message matching the specified matcher.
+     * You must have first called {@link #capture}.
+     *
+     * @param level The {@link Level} of the {@link LogRecorder} to match. Pass {@code null} to match any {@link Level}.
+     * @param message The matcher to match against {@link LogRecord#getMessage}.
+     */
+    public static Matcher<LogRecorder> recorded(@CheckForNull Level level, @NonNull Matcher<String> message) {
+        return recorded(level, message, null);
+    }
+
+    /**
+     * Creates a {@link Matcher} that matches if the {@link LogRecorder} has a {@link LogRecord}
+     * with a message matching the specified matcher and with a {@link Throwable} matching the specified
+     * matcher.
+     * You must have first called {@link #capture}.
+     *
+     * @param message the matcher to match against {@link LogRecord#getMessage}
+     * @param thrown the matcher to match against {@link LogRecord#getThrown()}. Passing {@code null} is equivalent to
+     * passing {@link org.hamcrest.Matchers#anything}
+     */
+    public static Matcher<LogRecorder> recorded(
+            @NonNull Matcher<String> message, @CheckForNull Matcher<Throwable> thrown) {
+        return recorded(null, message, thrown);
+    }
+
+    /**
+     * Creates a {@link Matcher} that matches if the {@link LogRecorder} has a {@link LogRecord}
+     * with a message matching the specified matcher.
+     * You must have first called {@link #capture}.
+     *
+     * @param message the matcher to match against {@link LogRecord#getMessage}
+     */
+    public static Matcher<LogRecorder> recorded(@NonNull Matcher<String> message) {
+        return recorded(null, message);
+    }
+
+    static class RecordedMatcher extends TypeSafeMatcher<LogRecorder> {
+        @CheckForNull
+        Level level;
+
+        @NonNull
+        Matcher<String> message;
+
+        @CheckForNull
+        Matcher<Throwable> thrown;
+
+        public RecordedMatcher(
+                @CheckForNull Level level, @NonNull Matcher<String> message, @CheckForNull Matcher<Throwable> thrown) {
+            this.level = level;
+            this.message = message;
+            this.thrown = thrown;
+        }
+
+        @Override
+        protected boolean matchesSafely(LogRecorder item) {
+            synchronized (item) {
+                for (LogRecord record : item.getRecords()) {
+                    if (level == null || record.getLevel() == level) {
+                        if (message.matches(record.getMessage())) {
+                            if (thrown != null) {
+                                if (thrown.matches(record.getThrown())) {
+                                    return true;
+                                }
+                            } else {
+                                return true;
+                            }
+                        }
+                    }
+                }
+            }
+            return false;
+        }
+
+        @Override
+        public void describeTo(Description description) {
+            description.appendText("has LogRecord");
+            if (level != null) {
+                description.appendText(" with level ");
+                description.appendValue(level.getName());
+            }
+            description.appendText(" with a message matching ");
+            description.appendDescriptionOf(message);
+            if (thrown != null) {
+                description.appendText(" with an exception matching ");
+                description.appendDescriptionOf(thrown);
+            }
+        }
+    }
+
+    /**
+     * Delegates to the given Handler but filter out records higher or equal to its initial level
+     */
+    private static class ConsoleHandlerWithMaxLevel extends ConsoleHandler {
+        private final Level initialLevel;
+
+        public ConsoleHandlerWithMaxLevel() {
+            super();
+            initialLevel = getLevel();
+        }
+
+        @Override
+        public void publish(LogRecord record) {
+            if (record.getLevel().intValue() < initialLevel.intValue()) {
+                super.publish(record);
+            }
+        }
+    }
+}