How to effectively test a method that returns a CompletableFuture in Java using JUnit 5?
I'm deploying to production and I've tried everything I can think of but I'm working on a Java application using Spring Boot (version 2.5.4) and I've come across a challenge while trying to unit test a method that returns a `CompletableFuture`. The method in question calls an external API asynchronously and returns the result wrapped in a `CompletableFuture`. Here's the method I need to test: ```java @Service public class ApiService { public CompletableFuture<String> fetchData() { return CompletableFuture.supplyAsync(() -> { // Simulating network call try { Thread.sleep(1000); } catch (InterruptedException e) { throw new RuntimeException(e); } return "data from API"; }); } } ``` I've tried writing a unit test using JUnit 5 and Mockito, but I'm having trouble with the asynchronous behavior. Here’s what I came up with: ```java @ExtendWith(MockitoExtension.class) public class ApiServiceTest { @InjectMocks private ApiService apiService; @Test public void testFetchData() throws Exception { CompletableFuture<String> futureResult = apiService.fetchData(); String result = futureResult.get(); // Blocking call assertEquals("data from API", result); } } ``` This test works, but it feels inefficient because of the blocking `get()` call and the artificial delay in the method. I’m concerned about the performance implications and how this might affect my test suite when running multiple tests. Are there better practices for testing asynchronous methods in JUnit 5? Should I be using `CompletableFuture`'s `join()` method instead? I also considered using `Mockito` to mock the asynchronous behavior, but I'm not sure how to implement that correctly without losing the real behavior of the method. Any insights would be greatly appreciated!