@Test
public void testDoFilter_occur_servletexception() throws IOException, ServletException {

    ServletException occurException = new ServletException("servlet exception.");
    doThrow(occurException).when(mockFilterChain).doFilter(mockRequest,
            mockResponse);
    try {
        testTarget.doFilter(mockRequest, mockResponse, mockFilterChain);
    } catch (ServletException e) {
        assertSame(occurException, e);
    }
    verify(mockExceptionLogger, times(1)).error(occurException);
}