Testing CORs in SpringBootTest

Im trying to write a test to verify our CORS settings. I configure CORS like this.

@Override
    public void configure(HttpSecurity httpSecurity) throws Exception {
//        super.configure(httpSecurity);
        httpSecurity.csrf().disable();
        httpSecurity.authorizeRequests().antMatchers("/**").permitAll();
        httpSecurity.cors();
    }

    @Bean
    public CorsConfigurationSource corsConfigurationSource() {
        CorsConfiguration configuration = new CorsConfiguration();
        List<String> allowedMethods = CORS_ALLOWED_METHODS;
        configuration.setAllowedMethods(allowedMethods);
        configuration.setAllowedOrigins(CORS_ALLOWED_ORIGINS);
        configuration.setAllowedHeaders(CORS_ALLOWED_HEADERS);
        configuration.setAllowCredentials(true);
        UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
        source.registerCorsConfiguration("/**", configuration);
        return source;
    }

I have verified with the debugger that CORS_ALLOWED_METHODS has values when my test runs.

Here is my test. It fails when I assert on the headers.

@RunWith(SpringRunner.class)
@SpringBootTest
@ActiveProfiles("dev")
public class ControllerTests {

    @Autowired
    private WebApplicationContext wac;

    public MockMvc mockMvc;

    @Before
    public void setup() {
        DefaultMockMvcBuilder builder = MockMvcBuilders
                .webAppContextSetup(this.wac)
                .apply(SecurityMockMvcConfigurers.springSecurity())
                .dispatchOptions(true);
        this.mockMvc = builder.build();
    }

    @Test
    public void testCors() throws Exception {
        this.mockMvc
                .perform(get("/test-cors"))
                .andDo(print())
                .andExpect(status().isOk())
                .andExpect(header().string("Access-Control-Allow-Methods", "OPTIONS,GET,HEAD,POST,PUT,DELETE,TRACE,CONNECT"))
                .andExpect(content().string("HAPPY\n"));
    }

    @SpringBootApplication(scanBasePackages = {"the.packages"})
    @Controller
    static class TestApplication {

        public static void main(String[] args) throws Exception {
            SpringApplication.run(TestApplication.class, args);
        }

        @RequestMapping(value = {"test-cors"},  method = RequestMethod.GET)
        @ResponseStatus(HttpStatus.OK)
        public @ResponseBody String testCors() {
            return "whatever";
        }
    }
}

As a note, when I actually run a SpringBoot app with this configuration we do get CORS headers.

Any help appreciated.