How to use the dojo.data.api.Identity function in dojo

runTest: function(datastore, t){
			// summary:
			//		Simple test of the getFeatures function of the store
			// description:
			//		Simple test of the getFeatures function of the store
			var store = new datastore(tests.data.readOnlyItemFileTestTemplates.getTestData("countries"));

			var features = store.getFeatures();
			t.assertTrue(features["dojo.data.api.Read"] != null);
			t.assertTrue(features["dojo.data.api.Identity"] != null);
		}
	},

function test_getFeatures(){
			// summary:
			//		Simple test of the getFeatures function of the store
			// description:
			//		Simple test of the getFeatures function of the store
			var store = new dojo.data.ItemFileWriteStore(tests.data.readOnlyItemFileTestTemplates.getTestData("countries"));

			var features = store.getFeatures();

			// make sure we have the expected features:
			doh.assertTrue(features["dojo.data.api.Read"] !== null);
			doh.assertTrue(features["dojo.data.api.Identity"] !== null);
			doh.assertTrue(features["dojo.data.api.Write"] !== null);
			doh.assertTrue(features["dojo.data.api.Notification"] !== null);
			doh.assertFalse(features["iggy"]);

			// and only the expected features:
			var count = 0;
			for(var i in features){
				doh.assertTrue((i === "dojo.data.api.Read" ||
					i === "dojo.data.api.Identity" ||
					i === "dojo.data.api.Write" ||
					i === "dojo.data.api.Notification"));
				count++;
			}
			doh.assertEqual(count, 4);
		},
		function testWriteAPI_setValue(){

_getIdentifierAttribute: function(){
		var identifierAttribute = this.getFeatures()['dojo.data.api.Identity'];
		// this._assert((identifierAttribute === Number) || (dojo.isString(identifierAttribute)));
		return identifierAttribute;
	},

postCreate: function(){
		// summary:
		//		sets up our event handling that we need for functioning
		//		as a select
		this.inherited(arguments);

		// Make our event connections for updating state
		this.connect(this, "onChange", "_updateSelection");

		// moved from startup
		//		Connects in our store, if we have one defined
		var store = this.store;
		if(store && (store.getIdentity || store.getFeatures()["dojo.data.api.Identity"])){
			// Temporarily set our store to null so that it will get set
			// and connected appropriately
			this.store = null;
			this.setStore(store, this._oValue);
		}
	},

_getIdentifierAttribute: function(){
		// this._assert((identifierAttribute === Number) || (dojo.isString(identifierAttribute)));
		return this.getFeatures()['dojo.data.api.Identity'];
	},

startup: function(){
		// summary:
		//		Connects in our store, if we have one defined
		this.inherited(arguments);
		var store = this.store, fetchArgs = {};
		dojo.forEach(["query", "queryOptions", "onFetch"], function(i){
			if(this[i]){
				fetchArgs[i] = this[i];
			}
			delete this[i];
		}, this);
		if(store && store.getFeatures()["dojo.data.api.Identity"]){
			// Temporarily set our store to null so that it will get set
			// and connected appropriately
			this.store = null;
			this.setStore(store, this._oValue, fetchArgs);
		}
	},

var fetchParentItems = dojo.hitch(this, function(/*item*/ item, /*function*/callback){
			// summary:
			//		Fetches the parent items for the given item
			var store = this.store, id;
			if(this.parentAttr && store.getFeatures()["dojo.data.api.Identity"] &&
				((id = this.store.getValue(item, this.parentAttr)) || id === "")){
				// Fetch by parent attribute
				var cb = function(i){
					if(store.getIdentity(i) == store.getIdentity(item)){
						callback(null);
					}else{
						callback([i]);
					}
				};
				if(id === ""){
					callback(null);
				}else if(typeof id == "string"){
					store.fetchItemByIdentity({identity: id, onItem: cb});
				}else if(store.isItem(id)){
					cb(id);
				}

this._storeRefPropName += "_";
		}
		while(allAttributeNames[this._itemNumPropName]){
			this._itemNumPropName += "_";
		}

		// Step 4: Some data files specify an optional 'identifier', which is 
		// the name of an attribute that holds the identity of each item. 
		// If this data file specified an identifier attribute, then build a 
		// hash table of items keyed by the identity of the items.
		var arrayOfValues;

		var identifier = dataObject.identifier;
		if(identifier){
			this._itemsByIdentity = {};
			this._features['dojo.data.api.Identity'] = identifier;
			for(i = 0; i < this._arrayOfAllItems.length; ++i){
				item = this._arrayOfAllItems[i];
				arrayOfValues = item[identifier];
				var identity = arrayOfValues[0];
				if(!this._itemsByIdentity[identity]){
					this._itemsByIdentity[identity] = item;
				}else{
					if(this._jsonFileUrl){
						throw new Error("dojo.data.ItemFileReadStore:  The json data as specified by: [" + this._jsonFileUrl + "] is malformed.  Items within the list have identifier: [" + identifier + "].  Value collided: [" + identity + "]");
					}else if(this._jsonData){
						throw new Error("dojo.data.ItemFileReadStore:  The json data provided by the creation arguments is malformed.  Items within the list have identifier: [" + identifier + "].  Value collided: [" + identity + "]");
					}
				}
			}
		}else{
			this._features['dojo.data.api.Identity'] = Number;

_getIdentifierAttribute: function(){
		var identifierAttribute = this.getFeatures()['dojo.data.api.Identity'];
		// this._assert((identifierAttribute === Number) || (dojo.isString(identifierAttribute)));
		return identifierAttribute;
	},

postMixInProperties: function(){
		this.tree = this;
		this.lastFocused = this.labelNode;

		this._itemNodeMap={};

		this._hideRoot = !this.label;

		if(!this.store.getFeatures()['dojo.data.api.Identity']){
			throw new Error("dijit.tree requires access to a store supporting the dojo.data Identity api");			
		}

		if(!this.cookieName){
			this.cookieName = this.id + "SaveStateCookie";
		}

		// if the store supports Notification, subscribe to the notification events
		if(this.store.getFeatures()['dojo.data.api.Notification']){
			this.connect(this.store, "onNew", "_onNewItem");
			this.connect(this.store, "onDelete", "_onDeleteItem");
			this.connect(this.store, "onSet", "_onSetItem");
		}
	},