text: import {any}                  from './helpers.es6.js';
  import {describeGraphClass}   from './graph-helpers.es6.js';
  import Graph                  from '../src/graph.es6.js';
  import addGraphOO             from '../src/addGraphOO.es6.js';
  import vertices_topologically from '../src/vertices_topologically.es6.js';
  
  let GraphOO = addGraphOO(Graph);
  Graph.plugin(vertices_topologically);
  
  describeGraphClass(GraphOO, () => {
  	describeMethod('vertices_topologically', () => {
  
  		// at this point, we can pretty much trust that this method works on GraphOO
  		// just as on Graph, so we're just making sure it yields graph.Vertex instances
  
  		it("yields graph.Vertex instances", () => {
  			for (let vertex of callItWith()) {
  				expect(vertex).toEqual(any(graph.Vertex));
  			}
  		});
  
  	});
  });
  