I would like to submit some code to help write unit tests that verify log behavior. Examples:

• Make sure that some code correctly logs errors and warnings
• The log messages contain the correct information (instead of, say, "[byte").
• Files are logged with absolute path
• Remove (expected) stack traces from test output

My code contains a class RedirectLogger which takes lists of classes or logger names and adds appenders to those which collect log events in a list.

At the end of the test, you can call a dump() method (optionally with a filter) to get everything that was logged.

Example code before Java 8:

RedirectLogger rl = new RedirectLogger(Tool.class, Util.class);
try {
    rl.install();

    tool.foo();
} finally  {
    rl.deinstall();
}

assertEquals("Expected log lines", rl.dump(Level.WARN));

Example > Java 8 with method that returns value:

RedirectLogger rl = new RedirectLogger(Tool.class, Util.class);
Type result = rl.with(() -> {
    return tool.bar();
});

assertEquals(..., result);
assertEquals("Expected log lines", rl.dump(Level.WARN));