@Test
    public void shouldGetSameInstance() {
        assertSame(mgr, SingleGremlinScriptEngineManager.instance());
        assertSame(mgr, SingleGremlinScriptEngineManager.instance());
        assertSame(mgr, SingleGremlinScriptEngineManager.instance());
        assertSame(mgr, SingleGremlinScriptEngineManager.instance());
        assertSame(mgr, SingleGremlinScriptEngineManager.instance());
    }
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/jsr223/SingleScriptEngineManagerTest.java