@Test
    public void shouldSupplyHashSetInstance() {
        assertEquals(0, HashSetSupplier.instance().get().size());
        assertThat(HashSetSupplier.instance().get(), instanceOf(HashSet.class));
    }
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/util/function/HashSetSupplierTest.java