fix(util): ensure ModelUtil#is never fails

lib/util/ModelUtil.js

@@ -11,7 +11,7 @@
 function is(element, type) {
   var bo = getBusinessObject(element);
 
-  return bo && bo.$instanceOf(type);
+  return bo && (typeof bo.$instanceOf === 'function') && bo.$instanceOf(type);
 }
 
 module.exports.is = is;

test/spec/util/ModelUtilSpec.js

@@ -0,0 +1,66 @@
+'use strict';
+
+require('../../TestHelper');
+
+/* global bootstrapModeler, inject */
+
+var coreModule = require('../../../lib/core'),
+    modelingModule = require('../../../lib/features/modeling');
+
+var ModelUtil = require('../../../lib/util/ModelUtil');
+
+
+describe('ModelUtil', function() {
+
+  var diagramXML = require('../../fixtures/bpmn/empty-definitions.bpmn');
+
+  beforeEach(bootstrapModeler(diagramXML, { modules: [ coreModule, modelingModule ] }));
+
+
+  it('should work with diagram element', inject(function(elementFactory) {
+
+    // given
+    var messageFlowConnection = elementFactory.createConnection({ type: 'bpmn:MessageFlow' });
+
+    // then
+    expect(ModelUtil.is(messageFlowConnection, 'bpmn:MessageFlow')).to.be.true;
+    expect(ModelUtil.is(messageFlowConnection, 'bpmn:BaseElement')).to.be.true;
+
+    expect(ModelUtil.is(messageFlowConnection, 'bpmn:SequenceFlow')).to.be.false;
+    expect(ModelUtil.is(messageFlowConnection, 'bpmn:Task')).to.be.false;
+  }));
+
+
+  it('should work with business object', inject(function(bpmnFactory) {
+
+    // given
+    var gateway = bpmnFactory.create('bpmn:Gateway');
+
+    // then
+    expect(ModelUtil.is(gateway, 'bpmn:Gateway')).to.be.true;
+    expect(ModelUtil.is(gateway, 'bpmn:BaseElement')).to.be.true;
+
+    expect(ModelUtil.is(gateway, 'bpmn:SequenceFlow')).to.be.false;
+  }));
+
+
+  it('should work with untyped business object', inject(function() {
+
+    // given
+    var foo = { businessObject: 'BAR' };
+
+    // then
+    expect(ModelUtil.is(foo, 'FOO')).to.be.false;
+  }));
+
+
+  it('should work with untyped diagram element', inject(function() {
+
+    // given
+    var foo = { };
+
+    // then
+    expect(ModelUtil.is(foo, 'FOO')).to.be.false;
+  }));
+
+});