CompletableFuture swallows exceptions?

The problem is you never request to receive the results of your call to linksCF.thenAccept(..).

Your call to linksCF.get() will wait for the results of the execution in your chain. But it will only return the results of then linksCF future. This doesn’t include the results of your assertion.

linksCF.thenAccept(..) will return a new CompletableFuture instance. To get the exception thrown call get() or check the exception status with isCompletedExceptionally() on the newly return CompletableFuture instance.

CompletableFuture<Void> acceptedCF = linksCF.thenAccept(list -> {
    assertThat(list, not(empty()));
});

acceptedCF.exceptionally(th -> {
    // will be executed when there is an exception.
    System.out.println(th);
    return null;
});
acceptedCF.get(); // will throw ExecutionException once results are available

Alternative?

CompletableFuture<List<String>> appliedCF = linksCF.thenApply(list -> {
    assertThat(list, not(empty()));
    return list;
});

appliedCF.exceptionally(th -> {
    // will be executed when there is an exception.
    System.out.println(th);
    return Coolections.emptyList();
});
appliedCF.get(); // will throw ExecutionException once results are available