fix(import): handle multiple DI elements per semantic

Closes #158

lib/import/BpmnTreeWalker.js

@@ -76,8 +76,12 @@ function BpmnTreeWalker(handler) {
     var bpmnElement = di.bpmnElement;
 
     if (bpmnElement) {
-      diRefs.bind(bpmnElement, 'di');
+      if (bpmnElement.di) {
-      bpmnElement.di = di;
+        logError('multiple DI elements defined for ' + elementToString(bpmnElement), { element: bpmnElement });
+      } else {
+        diRefs.bind(bpmnElement, 'di');
+        bpmnElement.di = di;
+      }
     } else {
       logError('no bpmnElement referenced in ' + elementToString(di), { element: di });
     }

test/fixtures/bpmn/error/multiple-dis.bpmn

@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<bpmn:definitions xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xmlns:bpmn="http://www.omg.org/spec/BPMN/20100524/MODEL"
+  xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI"
+  xmlns:dc="http://www.omg.org/spec/DD/20100524/DC"
+  xmlns:di="http://www.omg.org/spec/DD/20100524/DI"
+  xsi:schemaLocation="http://www.omg.org/spec/BPMN/20100524/MODEL BPMN20.xsd"
+  id="gateway-testcase"
+  targetNamespace="http://bpmn.io/schema/bpmn">
+  <bpmn:process id="Process_1">
+    <bpmn:inclusiveGateway id="InclusiveGateway_1"/>
+  </bpmn:process>
+  <bpmndi:BPMNDiagram id="BPMNDiagram_1">
+    <bpmndi:BPMNPlane id="BPMNPlane_1" bpmnElement="Process_1">
+      <bpmndi:BPMNShape id="_BPMNShape_InclusiveGateway_2" bpmnElement="InclusiveGateway_1">
+        <dc:Bounds height="50.0" width="50.0" x="114.0" y="99.0"/>
+      </bpmndi:BPMNShape>
+      <!-- second DI element for InclusiveGateway_1 -->
+      <bpmndi:BPMNShape id="_BPMNShape_InclusiveGateway_2" bpmnElement="InclusiveGateway_1">
+        <dc:Bounds height="50.0" width="50.0" x="114.0" y="129.0"/>
+      </bpmndi:BPMNShape>
+    </bpmndi:BPMNPlane>
+  </bpmndi:BPMNDiagram>
+</bpmn:definitions>

test/spec/import/ImporterSpec.js

@@ -277,6 +277,23 @@ describe('import - importer', function() {
       });
     });
 
+
+    it('should import multiple dis', function(done) {
+
+      // given
+      var xml = fs.readFileSync('test/fixtures/bpmn/error/multiple-dis.bpmn', 'utf8');
+
+      // when
+      runImport(diagram, xml, function(err, warnings) {
+
+        expect(warnings.length).toBe(1);
+        expect(warnings[0].message).toBe('multiple DI elements defined for <bpmn:InclusiveGateway id="InclusiveGateway_1" />');
+
+        done(err);
+      });
+    });
+
+
     it('should extend missing attribute with default value', function(done) {
 
       // given