public S loadHighestPriorityInstance() {
        load();

        if (sortedClassList.size() == 0) {
            return null;
        }

        Class<? extends S> highestClass = sortedClassList.get(0);
        return createInstance(highestClass);
    }
@Test
    public void testLoadHighestPriorityInstance() {
        ProcessorSlot slot = SpiLoader.of(ProcessorSlot.class).loadHighestPriorityInstance();
        assertNotNull(slot);

        // NodeSelectorSlot is highest order priority with @Spi(order = -10000) among all slots
        assertTrue(slot instanceof NodeSelectorSlot);
    }