static InputStream createDummyInputStream(int payloadSize) {
        Instant end = Instant.now().plusSeconds(60);
        return createDummyInputStream(payloadSize, ThreadLocalRandom.current(), () -> Instant.now().isBefore(end));
    }
Creates an input stream that spits out random documents (id and data) for one minute.
vespa-feed-client-cli/src/main/java/ai/vespa/feed/client/impl/CliClient.java