test(roundtrip): verify local namespaces are kept

This adds a test that verifies that locally re-declared namespaces are
kept (to keep diagram changes to a minimum).

Related to bpmn-io/bpmn-js#1310

test/fixtures/bpmn/namespace-redefinition.bpmn

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<definitions xmlns="http://www.omg.org/spec/BPMN/20100524/MODEL" id="Definitions" targetNamespace="http://bpmn.io">
+  <process id="Process_1">
+    <dataObjectReference xmlns="http://www.omg.org/spec/BPMN/20100524/MODEL" id="DataObjectReference_1" />
+    <foo:userTask xmlns:foo="http://www.omg.org/spec/BPMN/20100524/MODEL" id="Task_1" name="Task 1" />
+  </process>
+  <BPMNDiagram xmlns="http://www.omg.org/spec/BPMN/20100524/DI" id="BPMNDiagram_1">
+    <BPMNPlane xmlns="http://www.omg.org/spec/BPMN/20100524/DI" bpmnElement="Definitions" />
+  </BPMNDiagram>
+</definitions>

test/spec/xml/roundtrip.js

@@ -11,6 +11,10 @@ import {
   validate
 } from '../../xml-helper';
 
+import {
+  readFileSync as readFile
+} from 'fs';
+
 
 describe('bpmn-moddle - roundtrip', function() {
 
@@ -591,12 +595,31 @@ describe('bpmn-moddle - roundtrip', function() {
 
       // local namespace declaration is exported
       expect(xml).to.contain(
-        '<BPMNDiagram id="BPMNDiagram_1" xmlns="http://www.omg.org/spec/BPMN/20100524/DI">'
+        '<BPMNDiagram xmlns="http://www.omg.org/spec/BPMN/20100524/DI" id="BPMNDiagram_1">'
       );
 
       await validate(xml);
     });
 
+
+    it('local namespace exports', async function() {
+
+      // given
+      var expectedXML = readFile('test/fixtures/bpmn/namespace-redefinition.bpmn', 'utf8');
+
+      var {
+        rootElement
+      } = await fromFile('test/fixtures/bpmn/namespace-redefinition.bpmn');
+
+      // when
+      var {
+        xml
+      } = await toXML(rootElement, { format: true });
+
+      // then
+      expect(xml).to.eql(expectedXML);
+    });
+
   });