This post has helped me to send CSV output from a controller when the desired media type is specified as a URL parameter. Here’s my configuration class that does this:

import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.lang.NonNull;
import org.springframework.web.servlet.config.annotation.ContentNegotiationConfigurer;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

import com.fasterxml.jackson.databind.ObjectMapper;

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Autowired
    private ObjectMapper objectMapper;

    @Override
    public void configureContentNegotiation(@NonNull final ContentNegotiationConfigurer configurer) {
        configurer
                .favorParameter(true)
                .parameterName("format")
                .ignoreAcceptHeader(false)
                .defaultContentType(MediaType.APPLICATION_JSON)
                .mediaType("csv", MediaType.parseMediaType("application/csv"))
                .mediaType("xml", MediaType.APPLICATION_XML)
                .mediaType("json", MediaType.APPLICATION_JSON);
    }

    @Override
    public void extendMessageConverters(@NonNull List<HttpMessageConverter<?>> converters) {
        converters.add(new CsvConverter<>(objectMapper));
    }    
}

The class CsvConverter is as described in the SO post referenced above.

Now I am trying to write a test that verifies my Spring configuration is correct. My understanding of https://docs.spring.io/spring-framework/reference/testing/webtestclient.htm indicates I should be able to use bindToController to do this, as the required configuration should be loaded.

Here’s the essence of the test code I used:

@SpringBootTest()
@ActiveProfiles(profiles = "dev")
public class PersonControllerTest {
    @Test     
    public void testGetPersonEnrollmentReturnsCSVWhenFormatParameterPresent() {  
      var personController = new PersonController(
        classService, mock(PersonService.class), enrollmentService, attendanceService
      );
      WebTestClient client = WebTestClient.bindToController(personController).build();

      client.get()
        .uri("/api/person/get/enrollments/1?format=csv")
        .exchange()
        .expectStatus().isOk()
        .expectHeader().contentType("application/csv");  
  
    }
}

When this test is run, it fails since the content type is application/json instead of the expected application/csv. I have verified that the code in my WebConfig.java configuration is being executed.

If I change the creation of the WebClient to look like this:

WebTestClient client = WebTestClient.bindToServer().baseUrl("https://localhost:8080").build();

and test against the running server, I get the expected content type.

What am I missing using bindToController to make the test run without needing a running server?