@Test
    public void shouldReturnEmptyListIfIoKeyPresentButNoSerializer() {
        final FakeIoRegistry registry = new FakeIoRegistry();
        registry.register(GryoIo.class, Long.class, String.class);
        assertEquals(0, registry.find(GryoIo.class, Number.class).size());
    }
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/structure/io/IoRegistryTest.java