JUnit 5 vs JUnit 4 for Async Testing

What are the main differences between JUnit 5 and JUnit 4 for async testing?

JUnit 5 introduces better support for asynchronous testing with the CompletableFuture and Assertions classes, while JUnit 4 relies on @Test(timeout).

Can you give an example of how to use async testing in JUnit 5?

Sure! In JUnit 5, you can use CompletableFuture to test async code like this:

@Test
void testAsync() throws Exception {
    CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> "Hello");
    assertEquals("Hello", future.get());
}

Is there any performance difference between the two versions?

JUnit 5 is generally more efficient due to its modular architecture, but the performance difference in async testing specifically may not be significant.

What about compatibility with existing JUnit 4 tests?

JUnit 5 is designed to be backward compatible, so you can run JUnit 4 tests alongside JUnit 5 tests using the Vintage engine.