Untitled

 // Klasa z metodą odpowiadającą za pobieranie danych z endpointa

public class Posts {

    private static final String POSTS_API_URL = "https://jsonplaceholder.typicode.com/posts";

    public static List<PostDto> getPosts() throws IOException, InterruptedException {

        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder()
                .GET()
                .header("accept", "application/json")
                .uri(URI.create(POSTS_API_URL))
                .build();

        HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());

        ObjectMapper mapper = new ObjectMapper();

        List<PostDto> posts = mapper.readValue(response.body(), new TypeReference<>() {
        });

        if (posts != null || posts.size() > 0) {

            return posts;

        } else {
            throw new IOException("No posts");
        }
    }


    public static void main(String[] args) throws IOException, InterruptedException {

        System.out.println(getPosts());

    }
}

// testy

import org.junit.jupiter.api.Test;

import java.io.IOException;

import static org.junit.jupiter.api.Assertions.assertEquals;

class PostsTest {

    @Test
    void getPosts1() throws IOException, InterruptedException {

        Posts posts = new Posts();
        boolean expected = true;

        boolean actual = Posts.getPosts().size() > 0;

        assertEquals(expected, actual);
    }

    @Test
    void getPosts2() throws IOException, InterruptedException {

        Posts posts = new Posts();
        boolean expected = true;

        boolean actual = Posts.getPosts() != null;

        assertEquals(expected, actual);
    }

}