Allow Graph to be constructed with an array of entities

Useful for tests.

js/id/graph/graph.js

@@ -1,7 +1,15 @@
 iD.Graph = function(entities, annotation) {
     if (!(this instanceof iD.Graph)) return new iD.Graph(entities, annotation);
 
-    this.entities = entities || {};
+    if (_.isArray(entities)) {
+        this.entities = {};
+        for (var i = 0; i < entities.length; i++) {
+            this.entities[entities[i].id] = entities[i];
+        }
+    } else {
+        this.entities = entities || {};
+    }
+
     this.annotation = annotation;
 
     if (iD.debug) {

test/spec/graph/graph.js

@@ -1,21 +1,19 @@
-describe('Graph', function() {
+describe('iD.Graph', function() {
+    it("can be constructed with an entities Object", function () {
+        var entity = iD.Entity(),
+            graph = iD.Graph({'n-1': entity});
+        expect(graph.entity('n-1')).to.equal(entity);
+    });
 
-    describe('Construction and access', function() {
-        it('entity', function() {
-            var entities = { 'n-1': {
-                    type: 'node',
-                    loc: [-80, 30],
-                    id: 'n-1'
-                }
-            };
-            var graph = iD.Graph(entities, 'first graph');
-            expect(graph.entity('n-1')).to.equal(entities['n-1']);
-        });
+    it("can be constructed with an entities Array", function () {
+        var entity = iD.Entity(),
+            graph = iD.Graph([entity]);
+        expect(graph.entity(entity.id)).to.equal(entity);
+    });
 
-        it('annotation', function() {
-            var graph = iD.Graph({}, 'first graph');
-            expect(graph.annotation).to.equal('first graph');
-        });
+    it('can be constructed with an annotation', function() {
+        var graph = iD.Graph({}, 'first graph');
+        expect(graph.annotation).to.equal('first graph');
     });
 
     describe('operations', function() {