A chamada simulada RestTemplate retorna HTTP 500

Tenho a seguinte classe de controlador no meu aplicativo Spring Boot.

package com.tsdevelopment.springbootrest;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.client.RestTemplate;
import java.util.Arrays;
import java.util.List;

@RestController
public class SpringController {
    private List<String> myList = Arrays.asList("Item 1", "Item 2");

    @Autowired
    RestTemplate restTemplate;

    @GetMapping("/v1/resources")
    public ResponseEntity<List<String>> getAllResources(@RequestParam(required = false) String parameter){
        return ResponseEntity.ok(myList);
    }
    
    //API to API call
    @GetMapping("/v1/resources/inter-api-call")
    public ResponseEntity<List<String>> apiCall(){
        List<String> apiResponse = restTemplate.getForEntity("http://localhost:8083/v1/resources", List.class).getBody();
        return ResponseEntity.ok(apiResponse);
    }

}

E estou tentando testar isso com a seguinte classe:

package com.tsdevelopment.springbootrest;

import io.restassured.RestAssured;
import io.restassured.http.ContentType;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.Mockito;
import org.mockito.MockitoAnnotations;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.web.server.LocalServerPort;
import java.util.Arrays;
import java.util.List;
import org.hamcrest.Matchers;
import org.springframework.http.ResponseEntity;
import org.springframework.web.client.RestTemplate;

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class SpringControllerTest {
    @InjectMocks
    SpringController springController;

    @Mock
    RestTemplate restTemplate;

    @LocalServerPort
    private int port;

    @BeforeEach
    public void setUp(){
        RestAssured.port = port;
        MockitoAnnotations.openMocks(this);
    }

    @Test
    public void apiCall(){
        Mockito.when(restTemplate.getForEntity("http://localhost:8083/v1/resources", List.class)).thenReturn(ResponseEntity.ok(Arrays.asList("Item 1", "Item 2")));
        System.out.println("RestTemplate response: " + restTemplate.getForEntity("http://localhost:8083/v1/resources", List.class));
        System.out.println("Controller response: " + springController.apiCall());
        RestAssured.given()
            .when()
            .get("/v1/resources/inter-api-call")
            .then()
            .statusCode(200)
            .body("", Matchers.equalTo("[\"Item 1\",\"Item 2\"]"));
    }

}

Quando executo o teste ele falha. Os logs que recebo são:

Resposta do RestTemplate: <200 OK OK,[Item 1, Item 2],[]> Resposta do controlador: <200 OK OK,[Item 1, Item 2],[]>

E o log de erros do teste é:

java.lang.AssertionError: 1 expectativa falhou. Código de status esperado <200>, mas era <500>.