Problem testing a Bean with a List property

Hi guys so here is my project:

Two entities connected with each other over a @OneToMany relationship:

@Entity
public class Brand {
	
	@Id
	@GeneratedValue
    private Long id;
	
	@Column
	@NotNull(message = "Brand can not have empty name.")
    private String name;
	
	@Column
    private String description;
	
	@OneToMany(mappedBy="brand"
	, cascade= {CascadeType.DETACH,
			CascadeType.MERGE,
			CascadeType.PERSIST,
			CascadeType.REFRESH},
	fetch = FetchType.EAGER)	
	@OrderBy("price ASC") // order products by price
	private List<Product> productList;
   
    // getters and setter following here ...
}

@Entity
public class Product {
	
	@Id
	@GeneratedValue
    private Long id;
	
	@Column
	@NotNull(message = "Product can not have empty name.")
    private String name;
	
	@Column
    private Double price;
	
	@Column
    private Boolean onSale=false;
	
	@ManyToOne(cascade= {CascadeType.DETACH,
			CascadeType.MERGE,
			CascadeType.PERSIST,
			CascadeType.REFRESH})
    @JoinColumn(name="brand_id", nullable=false)
	private Brand brand;

 // getters and setter following here ...
}

package com.microservices.product.datatranferobject;

import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;


@JsonInclude(JsonInclude.Include.NON_NULL)
public class ProductDTO {
	
	private Long id;
	
    private String name;	
	
    private Double price;	
    
    @JsonIgnore // omit this property when exposing data over the API
    private Boolean onSale;
    
    private String event;
    
    public ProductDTO() {
    	
    }    

	public ProductDTO(Long id, String name, Double price, String event, Boolean onSale) {
		super();
		this.id = id;
		this.name = name;
		this.price = price;
		this.event = event;
		this.onSale=onSale;
	}
    
	public Boolean getOnSale() {
		return onSale;
	}

	public void setOnSale(Boolean onSale) {
		this.onSale = onSale;
	}

	public Long getId() {
		return id;
	}

	public void setId(Long id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Double getPrice() {
		return price;
	}

	public void setPrice(Double price) {
		this.price = price;
	}

	public String getEvent() {
		return onSale?"ON SALE":null;
	}

	public void setEvent(String event) {
		this.event = event;
	}    
	
}


public class BrandDTO {
	private String name;
	
	private List<ProductDTO> productList;
	
	public BrandDTO() {}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public List<ProductDTO> getProductList() {
		return productList;
	}

	public void setProductList(List<ProductDTO> productList) {
		this.productList = productList;
	}	
}

A simple DAO Class:

public interface BrandRepository extends JpaRepository<Brand, Long>{
	
	List<Brand> findAllByOrderByName();
}

A simple service:

public interface BrandService {

	List<Brand> getAllBrands();	
}

@Service
public class BrandServiceImpl implements BrandService {
	
	@Autowired
	BrandRepository myBrandRepo;
	
	@Override
	public List<Brand> getAllBrands(){
		return myBrandRepo.findAllByOrderByName();
	}	
}

and a controller which maps Products to ProductDTOs usinf my custom programmed Mapper:

public class ModelMapper {
	public static BrandDTO makeBrandDTO(Brand myBrand)
    {
		BrandDTO myBrandDTO=new BrandDTO();
		
		org.modelmapper.ModelMapper myStandardMapper=new org.modelmapper.ModelMapper();
		
		List<ProductDTO> myProductsList=myBrand.getProductList()
				.stream()
				.map(product->myStandardMapper.map(product, ProductDTO.class))
				.collect(Collectors.toList());
		myBrandDTO.setProductList(myProductsList);
		
		myBrandDTO.setName(myBrand.getName());
		
        return myBrandDTO;
    }
}


@RestController
@RequestMapping("v1/search")
public class BrandController {
	
	@Autowired
	BrandService myBrandService;
	
	@GetMapping("/get/products/")
	public Map<String, List<ProductDTO>> getAllProductsMap(){
		
		List<BrandDTO> myList= myBrandService.getAllBrands()
		.stream().map(brand->ModelMapper.makeBrandDTO(brand))
		.collect(Collectors.toList());		
		
		Map<String, List<ProductDTO>> myMap=new TreeMap<String, List<ProductDTO>> ();
		
		myList.forEach(brand->myMap.put(brand.getName(), brand.getProductList()));
		
		return myMap;
	}
	
}

ProductDTO is quite the same as Product entity so I will spare the time ans space writing it down.

So here comes the Problem. I am using Junit to test my Controller having the following class run the test:

@RunWith(SpringRunner.class)
@SpringBootTest(classes = ProductApplication.class,webEnvironment=WebEnvironment.RANDOM_PORT)
public class ControllerLayerTester {
	
	private static Log myLogger = LogFactory.getLog(ControllerLayerTester.class);
	
    private static RestTemplate restTemplate;
	
	private static HttpHeaders headers;
	
	@LocalServerPort
    private int port;
	
	@BeforeClass
	public static void runBeforeAllTestMethods() {
	 
	    restTemplate = new RestTemplate();
	    headers = new HttpHeaders();
	    headers.setContentType(MediaType.APPLICATION_JSON);
	    
	}
	
	/**
     * simple test to verify the given requirements
     */
	@Test
	public void testBrandListIsOrdered() {
		
		TreeMap<String, List<ProductDTO>> productList=restTemplate.getForObject("http://localhost:"+port+"/v1/search/get/products/",TreeMap.class);
		
		for (List<ProductDTO> myProductList:productList.values()) {
			
			myProductList.forEach(product->assertTrue(product.getId()!=null));
					
		}
	}

}

And when I run it I get the following error:

java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.microservices.product.datatranferobject.ProductDTO
	at java.util.ArrayList.forEach(ArrayList.java:1257)
	at com.microservices.product.ControllerLayerTester.testBrandListIsOrdered(ControllerLayerTester.java:81)

Am I doing something wrong here ? Why am I not getting the List filled with my entities but instead filled with LinkedHashMaps? Is there a solution in order to get a List of Products?

EDIT:

I am also providing here my project dependencies and I added on top of my post also the DTOs:

buildscript {
	ext {
		springBootVersion = '2.1.0.RELEASE'
	}
	repositories {
		mavenCentral()
	}
	dependencies {
		classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
	}
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'

group = 'com.microservices'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 1.8

repositories {
	mavenCentral()
}


dependencies {
	implementation('org.springframework.boot:spring-boot-starter-data-jpa')
	implementation('org.springframework.boot:spring-boot-starter-web')
	compile("org.springframework.boot:spring-boot-devtools")
	compile group: 'org.modelmapper', name: 'modelmapper', version: '2.1.0'
	runtimeOnly('com.h2database:h2')
	testImplementation('org.springframework.boot:spring-boot-starter-test')
	testImplementation 'org.assertj:assertj-core:3.15.0'
	compile group: 'com.google.guava', name: 'guava', version: '23.5-jre'
	compile group: 'io.springfox', name: 'springfox-swagger2', version: '2.7.0'
	compile group: 'io.springfox', name: 'springfox-swagger-ui', version: '2.7.0' 
}

The problem is that parameterization of TreeMap<String, List<ProductDTO>> cannot be inferred from TreeMap.class inside restTemplate.getForObject(...)

You'll want to use the more generic version:

restTemplate.exchange(
    "http://localhost:"+port+"/v1/search/get/products/",
    HttpMethod.GET,
    new HttpEntity<>(null, headers),
    new ParameterizedTypeReference<TreeMap<String, List<ProductDTO>>() {}
)