public static TeeStream ofSystemErr() {
        TeeStream teed = new TeeStream(System.err);
        System.setErr(new PrintStream(teed));
        return teed;
    }
Used to replace System.out and System.err, providing the ability to forward output to an additional sink.

@author jonmv
vespa-osgi-testrunner/src/main/java/com/yahoo/vespa/testrunner/TeeStream.java