question: private String stackTraceStr ( final Throwable error ) { if ( error == null ) { return "" ; } StringWriter sw = new StringWriter ( ) ; PrintWriter pw = new PrintWriter ( sw ) ; error . printStackTrace ( pw ) ; pw . close ( ) ; return sw . toString ( ) ; }
target:  Grab the stack trace into a string since the exception was thrown in a thread and we want the assert  outside the thread to show the stack trace in case of failure.   