Testing web layer Spring Boot

Just made a controller in Spring Boot and I want to unit test it.

The code of the controller and its method is:

@Controller
@RequestMapping("/projects/{pid}/clusters")
public class ClusterController {

    @Autowired
    private ClusterService clusterService;

    @Autowired
    private ProjectService projectService;


    @RequestMapping(method = RequestMethod.GET)
    public String getAllClusters(@PathVariable("pid") Integer projectId, Model model){
        Project project = this.projectService.getProjectById(projectId);
        Set<Cluster> clusters = project.getClusters();
        model.addAttribute("projectID", projectId);
        model.addAttribute("clusters", clusters);
        return "clusters";
    }

This method simply returns a view (HTML) when a user gets to a specific URL.

Code of my test:

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class clusterControllerTest {

    @LocalServerPort
    private int port;

    private URL base;

    @Autowired
    private TestRestTemplate testRestTemplate;

    @Before
    public void setUp() throws Exception{
    }

    @Test
    public void getCluster() throws Exception{
        this.base = new URL("http://localhost:" + port + "/projects/1/clusters");
        ResponseEntity<String> response = testRestTemplate.getForEntity(base.toString(), String.class);
        assertThat(response.getBody(), equalTo("clusters"));

    }
}

I'm already testing my repository and service layer in other tests. I only want to get the right return when navigating to a specific URL (which calls a specific method in de Controller).

In my examply when someone goes to "http://localhost:" + port + "/projects/1/clusters" The Controller should return "clusters".

When I execute this code I get the error that says my assertThat went wrong. Because "clusters" is compared to the whole html page.

How can I easily just test the return string of my controller? I don't have much experience with testing. Much thanks in advance!