added missing_tag test

test/index.html

@@ -143,6 +143,7 @@
     <script src='spec/util/session_mutex.js'></script>
     <script src='spec/util/util.js'></script>
 
+    <script src='spec/validations/missing_tag.js'></script>
     <script src='spec/operations/detach_node.js'></script>
     <script>
         window.mocha.run();

test/spec/validations/missing_tag.js

@@ -0,0 +1,43 @@
+describe('iD.validations.missing_tag', function () {
+    var context;
+
+    beforeEach(function() {
+        context = iD.Context();
+    });
+
+    function createInvalidWay() {
+        var n1 = iD.Node({id: 'n-1', loc: [4,4]});
+        var n2 = iD.Node({id: 'n-2', loc: [4,5]});
+
+        var w = iD.Way({id: 'w-1', nodes: ['n-1', 'n-2']});
+
+        context.perform(
+            iD.actionAddEntity(n1),
+            iD.actionAddEntity(n2),
+            iD.actionAddEntity(w)
+        );
+    }
+
+    function validate() {
+        var validator = iD.validationMissingTag();
+        var changes = context.history().changes();
+        return validator(changes, context.graph());
+    }
+
+    it('has no errors on init', function() {
+        var issues = validate();
+        expect(issues).to.have.lengthOf(0);
+    });
+
+    it('finds missing tags', function() {
+        createInvalidWay();
+        var issues = validate();
+        expect(issues).to.have.lengthOf(1);
+        var issue = issues[0];
+        expect(issue.type).to.eql(iD.ValidationIssueType.missing_tag);
+        expect(issue.entities).to.have.lengthOf(1);
+        expect(issue.entities[0].id).to.eql('w-1');
+    });
+
+
+});