Testing Spring (WebTestClient/JUnit)

Intro

JUnit essentials

Code: assertion idea

public class Main {
  // Simple, runnable demo of assertion-like checks (not JUnit), prints PASS/FAIL.
  static void assertEquals(int expected, int actual, String name) {
    if (expected == actual) {
      System.out.println(name + ": PASS");
    } else {
      System.out.println(name + ": FAIL expected " + expected + " but was " + actual);
    }
  }
  public static void main(String[] args) {
    // Pretend we test a controller method that adds numbers.
    int sum = 2 + 3; // pretend controller result
    assertEquals(5, sum, "addsTwoNumbers");
  }
}

WebTestClient overview

Code: request→verify flow

public class Main {
  // Simulate an HTTP test: build request, call handler, verify response.
  static String handleHello(String path) {
    // pretend controller:
    if ("/hello".equals(path)) return "Hello";
    return "404";
  }
  public static void main(String[] args) {
    String response = handleHello("/hello");
    if ("Hello".equals(response)) {
      System.out.println("GET /hello -> 200 OK, body=Hello (PASS)");
    } else {
      System.out.println("GET /hello -> FAIL");
    }
  }
}

Code: verify error path

public class Main {
  // Simulate verifying error responses.
  static int deleteUser(long id) {
    // pretend service: only id 1 exists
    if (id == 1L) return 204; // No Content
    return 404; // Not Found
  }
  public static void main(String[] args) {
    int status = deleteUser(99L); // should be 404 in our scenario
    if (status == 404) {
      System.out.println("DELETE /users/99 -> 404 (PASS)");
    } else {
      System.out.println("DELETE /users/99 -> FAIL got " + status);
    }
  }
}

WebTestClient check

Recap