Added JenkinsRule.showAgentLogs utility

pom.xml

@@ -28,7 +28,8 @@ THE SOFTWARE.
   <parent>
     <groupId>org.jenkins-ci</groupId>
     <artifactId>jenkins</artifactId>
-    <version>1.49</version>
+    <version>1.51</version>
+    <relativePath />
   </parent>
 
   <groupId>org.jenkins-ci.main</groupId>

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

@@ -223,8 +223,10 @@
 import java.nio.channels.ClosedByInterruptException;
 import java.util.concurrent.ExecutionException;
 import java.util.logging.ConsoleHandler;
+import java.util.logging.Formatter;
 import java.util.logging.Handler;
 import jenkins.model.ParameterizedJobMixIn;
+import jenkins.security.MasterToSlaveCallable;
 import org.hamcrest.core.IsInstanceOf;
 import org.junit.rules.DisableOnDebug;
 import org.junit.rules.Timeout;
@@ -988,6 +990,53 @@ public void waitOnline(Slave s) throws Exception {
         }
     }
 
+    /**
+     * Same as {@link #showSlaveLogs(Slave, Map)} but taking a preconfigured list of loggers as a convenience.
+     */
+    public void showSlaveLogs(Slave s, LoggerRule loggerRule) throws Exception {
+        showSlaveLogs(s, loggerRule.getRecordedLevels());
+    }
+
+    /**
+     * Forward agent logs to standard error of the test process.
+     * Otherwise log messages would be sent only to {@link Computer#getLogText} etc.,
+     * or discarded entirely (if below {@link Level#INFO}).
+     * @param s an <em>online</em> agent
+     * @param loggers {@link Logger#getName} tied to log level
+     */
+    public void showSlaveLogs(Slave s, Map<String, Level> loggers) throws Exception {
+        s.getChannel().call(new RemoteLogDumper(s.getNodeName(), loggers));
+    }
+
+    private static final class RemoteLogDumper extends MasterToSlaveCallable<Void, RuntimeException> {
+        private final String name;
+        private final Map<String, Level> loggers;
+        private final TaskListener stderr = StreamTaskListener.fromStderr();
+        RemoteLogDumper(String name, Map<String, Level> loggers) {
+            this.name = name;
+            this.loggers = loggers;
+        }
+        @Override public Void call() throws RuntimeException {
+            Handler handler = new Handler() {
+                final Formatter formatter = new SupportLogFormatter();
+                @Override public void publish(LogRecord record) {
+                    if (isLoggable(record)) {
+                        stderr.getLogger().print(formatter.format(record).replaceAll("(?m)^", "[" + name + "] "));
+                    }
+                }
+                @Override public void flush() {}
+                @Override public void close() throws SecurityException {}
+            };
+            handler.setLevel(Level.ALL);
+            loggers.entrySet().forEach(e -> {
+                Logger logger = Logger.getLogger(e.getKey());
+                logger.setLevel(e.getValue());
+                logger.addHandler(handler);
+            });
+            return null;
+        }
+    }
+
     /**
      * Blocks until the ENTER key is hit.
      * This is useful during debugging a test so that one can inspect the state of Hudson through the web browser.

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

@@ -36,6 +36,7 @@
 import java.util.logging.LogRecord;
 import java.util.logging.Logger;
 import java.util.logging.SimpleFormatter;
+import java.util.stream.Collectors;
 import javax.annotation.CheckForNull;
 import javax.annotation.Nonnull;
 import org.hamcrest.Matcher;
@@ -138,6 +139,10 @@ public LoggerRule 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}.