code: @Test public void exceptionErrorWithCommittedResponse() throws Exception {
    this.filter.addErrorPages(new ErrorPage(RuntimeException.class,"/500"));
    this.chain=new MockFilterChain(){
      @Override public void doFilter(    ServletRequest request,    ServletResponse response) throws IOException, ServletException {
        super.doFilter(request,response);
        response.flushBuffer();
        throw new RuntimeException("BAD");
      }
    }
  ;
    this.filter.doFilter(this.request,this.response,this.chain);
    assertThat(this.response.getForwardedUrl(),is(nullValue()));
  }
  