How do you test code that uses parallel streams?

Testing code that utilizes parallel streams can be a bit challenging due to the inherent concurrency and non-deterministic behavior of parallel processing. To properly test such code, it is essential to ensure that tests can run in an environment that manages the threads effectively and maintains accuracy in assertions. Here’s an approach you can use to test code with parallel streams:

// Example of a method using parallel streams
public List processParallel(List input) {
    return input.parallelStream()
                .map(String::toUpperCase)
                .collect(Collectors.toList());
}

// Test using JUnit
@Test
public void testProcessParallel() {
    List input = Arrays.asList("apple", "banana", "cherry");
    List expected = Arrays.asList("APPLE", "BANANA", "CHERRY");
    
    List result = processParallel(input);
    
    assertEquals(expected, result);
}