How should I test Servlet Filters?

Question

having trouble figuring out how to test my servlet filters

@Component
@Order( Ordered.HIGHEST_PRECEDENCE )
class CORSFilter extends OncePerRequestFilter {
    private final Logger log = LoggerFactory.getLogger( CORSFilter.class );

    @Override
    protected void doFilterInternal(
            final HttpServletRequest request,
            final HttpServletResponse response,
            final FilterChain filterChain )
            throws ServletException, IOException {
        log.debug( "request: {}", request );
        response.setHeader( "Access-Control-Allow-Origin", "*" );
        response.setHeader( "Access-Control-Allow-", "POST, GET, PUT, OPTIONS, DELETE" );
        response.setHeader( "Access-Control-Allow-Headers", "content-type, x-auth-token, x-requested-with" );
        response.setHeader( "Access-Control-Expose-Headers", "Location" );
        response.setIntHeader( "Access-Control-Max-Age", 3600 );
        filterChain.doFilter( request, response );
    }
}

here's what I've tried writing test wise

@RunWith( SpringJUnit4ClassRunner.class )
@WebAppConfiguration
@ComponentScan( "com.xenoterracide.rpf.infrastructure.http")
@SpringApplicationConfiguration( classes = { MockServletContext.class } )
public class TestHeaders {

    @Autowired
    private WebApplicationContext context;
    private MockMvc               mockMvc;

    @Before
    public void setup() {
        this.mockMvc = MockMvcBuilders.webAppContextSetup( context ).build();
    }

    @Test
    public void testCORS() throws Exception {
        this.mockMvc.perform( options( "/" ) )
                    .andExpect( status().is2xxSuccessful() )
                    .andExpect( header().string( "Access-Control-Allow-Origin",
                            allOf( notNullValue(), instanceOf( String.class ) ) ) );
    }

}

here's my test error

java.lang.AssertionError: Response header Access-Control-Allow-Origin
Expected: (not null and an instance of java.lang.String)
 but: not null was null

how can I test that my servlet filters are functioning correctly? bonus points if testing them doesn't require loading the full context, db and all.

Answer 1

You can register a Filter instance in your MockMvc

this.mockMvc = MockMvcBuilders.webAppContextSetup( context )
                              .addFilter(new CORSFilter(), "/*")
                              .build();