@Test(expected = IllegalArgumentException.class)
    public void shouldFailMergeEForBadInput() {
        g.mergeE(CollectionUtil.asMap(T.value, "nope"));
    }
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversalSourceTest.java