Currently, if one has a command-line application with multiple subcommands, and one wants to write a high-level help message to the console, they would write something like this:

String... args = ...;
CommandLine cmd = ...;
cmd.parseWithHandler(new RunLast(), System.out, args);

or if things are a bit more complicated (as is the case for me):

String... args = ...;
CommandLine cmd = ...;
try {
  List<CommandLine> parsedArgs = cmd.parse(args);
  new RunLast().handleParseResult(parsedArgs, System.out, Ansi.AUTO);
  System.exit(0);
} catch (ParameterException exception) {
  new DefaultExceptionHandler()
      .handleException(exception, System.err, Ansi.AUTO, args);
  System.exit(-1);
}

But sadly, this is not quite enough for me, because I need some way of "intercepting" the text sent to System.{out,err} so that I can assert on the contents of auto-generated help message at unit-test time.

The closest solution I've thought of so far is to use PrintWriters in place of System.{out,err} so that, at unit-test time, I can swap out System.{out,err} with a custom PrintWriter that diverts the text it receives to a StringWriter, so that I can query the text directly. But sadly, this doesn't work because RunLast::handleParseResult doesn't have an overload that accepts a PrintWriter instead of a PrintStream.

Does picocli have something built-in that would allow me to intercept the auto-generated help message of a command-line application with multiple subcommands?

If not, would providing an overload of IParseResultHandler::handleParseResult that accepts a PrintWriter be an idea that the picocli team would be interested in implementing?