Spring Boot TestRestTemplate return null body - spring-boot

Question

Havin a quite very simple test class followed by a video tut:
#SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
public class TestClassTest {
#LocalServerPort
private int port;
#Autowired
private TestRestTemplate testRestTemmplate;
#Test
public void test_one() {
String url = "http://localhost:" + port + "/v1/read";
UriComponents builder = UriComponentsBuilder.fromHttpUrl(url).build();
HttpHeaders headers = new HttpHeaders();
headers.set("accept", "application/json");
HttpEntity<String> requestEntity = new HttpEntity<>(null, headers);
ResponseEntity<String> response = testRestTemmplate.exchange(builder.toString(), HttpMethod.GET, requestEntity, String.class);
System.out.println(response.getBody());
assertEquals(HttpStatus.OK, response.getStatusCode());
}
}
The underlying controller class for test looks like:
#RestController
public class TestController {
#RequestMapping(value = "/v1/read", method = RequestMethod.GET, produces = "application/json")
public ResponseEntity<String> data() {
return ResponseEntity.status(HttpStatus.OK).header("status", "completed").body("fertig!");
}
}
Some issues i wondering with:
Running the test will evaluate to green thats fine but if i change the url in the test it will be also OK
The body from response is null and
the header i set within the ResponseEntity is no part of the response from testResttemplate.
Where are my misunderstandings?
Edit: here are my imports:
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.boot.test.web.client.TestRestTemplate;
import org.springframework.boot.test.web.server.LocalServerPort;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.ResponseEntity;
import org.springframework.web.util.UriComponents;
import org.springframework.web.util.UriComponentsBuilder;
As seen this are only the "standard" import coming from spring dependencies. Nothing exotics.