diff --git a/lib/import/BpmnTreeWalker.js b/lib/import/BpmnTreeWalker.js
index b001bd7c..db8210d7 100644
--- a/lib/import/BpmnTreeWalker.js
+++ b/lib/import/BpmnTreeWalker.js
@@ -10,6 +10,7 @@ import {
   elementToString
 } from './Util';
 
+// TODO: should be configurable: true as well which would allow to remove binding
 var diRefs = new Refs({ name: 'bpmnElement', enumerable: true }, { name: 'di' });
 
 /**
@@ -230,7 +231,7 @@ export default function BpmnTreeWalker(handler, translate) {
     handleDeferred(deferred);
   }
 
-  function handleDeferred(deferred) {
+  function handleDeferred() {
 
     var fn;
 
@@ -453,6 +454,9 @@ export default function BpmnTreeWalker(handler, translate) {
   // API //////////////////////
 
   return {
-    handleDefinitions: handleDefinitions
+    handleDeferred: handleDeferred,
+    handleDefinitions: handleDefinitions,
+    handleSubProcess: handleSubProcess,
+    registerDi: registerDi
   };
 }
\ No newline at end of file
diff --git a/test/spec/import/BpmnTreeWalkerSpec.js b/test/spec/import/BpmnTreeWalkerSpec.js
new file mode 100644
index 00000000..6fcde912
--- /dev/null
+++ b/test/spec/import/BpmnTreeWalkerSpec.js
@@ -0,0 +1,176 @@
+/* global sinon */
+
+import BpmnTreeWalker from 'lib/import/BpmnTreeWalker';
+
+import BpmnModdle from 'bpmn-moddle';
+
+import { find } from 'min-dash';
+
+import simpleXML from 'test/fixtures/bpmn/simple.bpmn';
+
+
+describe('import - BpmnTreeWalker', function() {
+
+  it('should expose functions', function() {
+
+    // when
+    const walker = createWalker();
+
+    // then
+    expect(walker.handleDeferred).to.exist;
+    expect(walker.handleDefinitions).to.exist;
+    expect(walker.handleSubProcess).to.exist;
+    expect(walker.registerDi).to.exist;
+  });
+
+
+  it('should walk bpmn:Definitions', function(done) {
+
+    // given
+    const elementSpy = sinon.spy(),
+          rootSpy = sinon.spy(),
+          errorSpy = sinon.spy();
+
+    const walker = createWalker({
+      element: elementSpy,
+      root: rootSpy,
+      error: errorSpy
+    });
+
+    createModdle(simpleXML, (err, definitions, context, moddle) => {
+
+      // when
+      walker.handleDefinitions(definitions);
+
+      // then
+      expect(elementSpy.callCount).to.equal(8);
+      expect(rootSpy.calledOnce).to.be.true;
+      expect(errorSpy.notCalled).to.be.true;
+
+      done();
+    });
+  });
+
+
+  it('should walk bpmn:SubProcess', function(done) {
+
+    // given
+    const elementSpy = sinon.spy(),
+          rootSpy = sinon.spy(),
+          errorSpy = sinon.spy();
+
+    const walker = createWalker({
+      element: elementSpy,
+      root: rootSpy,
+      error: errorSpy
+    });
+
+    createModdle(simpleXML, (err, definitions, context, moddle) => {
+      const subProcess = findElementWithId(definitions, 'SubProcess_1');
+
+      const plane = definitions.diagrams[0].plane,
+            planeElements = plane.planeElement;
+
+      // register DI
+      planeElements.forEach(walker.registerDi);
+
+      // when
+      walker.handleSubProcess(subProcess);
+
+      walker.handleDeferred();
+
+      // then
+      expect(elementSpy.callCount).to.equal(3);
+      expect(rootSpy.notCalled).to.be.true;
+      expect(errorSpy.notCalled).to.be.true;
+
+      done();
+    });
+  });
+
+
+  it('should error', function(done) {
+
+    // given
+    const elementSpy = sinon.spy(),
+          rootSpy = sinon.spy(),
+          errorSpy = sinon.spy();
+
+    const walker = createWalker({
+      element: elementSpy,
+      root: rootSpy,
+      error: errorSpy
+    });
+
+    createModdle(simpleXML, (err, definitions, context, moddle) => {
+
+      const element = findElementWithId(definitions, 'SubProcess_1');
+
+      // will error
+      element.di = 'DI';
+
+      // when
+      walker.handleDefinitions(definitions);
+
+      // then
+      expect(elementSpy.callCount).to.equal(8);
+      expect(rootSpy.calledOnce).to.be.true;
+      expect(errorSpy.calledOnce).to.be.true;
+
+      done();
+    });
+  });
+
+});
+
+
+// helpers //////////
+
+function createModdle(xml, done) {
+  const moddle = new BpmnModdle();
+
+  moddle.fromXML(xml, 'bpmn:Definitions', (err, definitions, context) => {
+    done(err, definitions, context, moddle);
+  });
+}
+
+function createWalker(listeners = {}) {
+  const visitor = {
+    element(element, parent) {
+      listeners.element && listeners.element(element, parent);
+    },
+    root(root) {
+      listeners.root && listeners.root(root);
+    },
+    error(message, context) {
+      listeners.error && listeners.error(message, context);
+    }
+  };
+
+  return new BpmnTreeWalker(visitor, function() {});
+}
+
+function findElementWithId(definitions, id) {
+
+  function findElement(element) {
+    if (element.id === id) {
+      return element;
+    }
+
+    if (element.flowElements) {
+      return find(element.flowElements, flowElement => {
+        const foundElement = findElement(flowElement);
+
+        return foundElement && foundElement.id === id;
+      });
+    }
+  }
+
+  return definitions.rootElements.reduce((foundElement, rootElement) => {
+    if (rootElement.id === id) {
+      return rootElement;
+    } else {
+      return findElement(rootElement) || foundElement;
+    }
+  }, null);
+}
\ No newline at end of file