code: public void setOut(PrintStream out) {
      this.out = out;
      if (!(System.out instanceof ThreadLocalPrintStream)) {
        throw new IllegalStateException("System.out should be set by nailgun.");
      }
      ThreadLocalPrintStream tls = (ThreadLocalPrintStream) System.out;
      tls.init(out);
    }
docs: Sets the current {@link PrintStream} for standard output for the current nail.
  
  @param out The {@link PrintStream} to use as stdout for the current nail. This should be a
  PrintStream that ultimately writes to {@link NGOutputStream}.