diff --git a/.eslintrc.json b/.eslintrc.json
index 52e1d7ce5c..de64bd22f8 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -1,7 +1,7 @@
 {
   "extends": "eslint:recommended",
   "parserOptions": {
-    "ecmaVersion": 2017
+    "ecmaVersion": 6
   },
   "rules": {
     "no-console": "off",
diff --git a/test/unit/path-effects.html b/test/unit/path-effects.html
index bb90c1db3d..156e3d4a95 100644
--- a/test/unit/path-effects.html
+++ b/test/unit/path-effects.html
@@ -49,7 +49,7 @@
     document.body.removeChild(el);
   });
 
-  async function verifyObserverOutput(nestingLevel, nested) {
+  function verifyObserverOutput(nestingLevel, nested, done) {
     assert.equal(el.computed, '[' + nested.obj.value + ']');
     assert.equal(el.nestedChanged.callCount, nestingLevel == 0 ? 1 : 0);
     if (nestingLevel == 0) {
@@ -105,9 +105,12 @@
         assert.equal(el.$.forward.objSubpathChanged.firstCall.args[0].value, nested.obj);
         assert.equal(el.$.forward.$.compose.objSubpathChanged.firstCall.args[0].path, 'obj');
         assert.equal(el.$.forward.$.compose.objSubpathChanged.firstCall.args[0].value, nested.obj);
-        await Promise.resolve(); // x-pe uses async PropertiesChanged
-        assert.equal(el.$.pe._propertiesChanged.callCount, 1);
-        assert.equal(el.$.pe._propertiesChanged.firstCall.args[1].obj, nested.obj);
+        // x-pe uses async PropertiesChanged
+        Promise.resolve().then(() => {
+          assert.equal(el.$.pe._propertiesChanged.callCount, 1);
+          assert.equal(el.$.pe._propertiesChanged.firstCall.args[1].obj, nested.obj);
+          done();
+        });
         break;
       case 1:
         assert.equal(el.nestedSubpathChanged.firstCall.args[0].path, 'nested.obj');
@@ -120,9 +123,12 @@
         assert.equal(el.$.forward.objSubpathChanged.firstCall.args[0].value, nested.obj);
         assert.equal(el.$.forward.$.compose.objSubpathChanged.firstCall.args[0].path, 'obj');
         assert.equal(el.$.forward.$.compose.objSubpathChanged.firstCall.args[0].value, nested.obj);
-        await Promise.resolve(); // x-pe uses async PropertiesChanged
-        assert.equal(el.$.pe._propertiesChanged.callCount, 1);
-        assert.equal(el.$.pe._propertiesChanged.firstCall.args[1].obj, nested.obj);
+        // x-pe uses async PropertiesChanged
+        Promise.resolve().then(() => {
+          assert.equal(el.$.pe._propertiesChanged.callCount, 1);
+          assert.equal(el.$.pe._propertiesChanged.firstCall.args[1].obj, nested.obj);
+          done();
+        });
         break;
       case 2:
         assert.equal(el.nestedSubpathChanged.firstCall.args[0].path, 'nested.obj.value');
@@ -135,16 +141,19 @@
         assert.equal(el.$.forward.objSubpathChanged.firstCall.args[0].value, 42);
         assert.equal(el.$.forward.$.compose.objSubpathChanged.firstCall.args[0].path, 'obj.value');
         assert.equal(el.$.forward.$.compose.objSubpathChanged.firstCall.args[0].value, 42);
-        await Promise.resolve(); // x-pe uses async PropertiesChanged
-        // Note the PropertiesMixin element only sees a deep set to 'nested.obj.value'
-        // because it overrides _shouldPropertyChange to allow object re-sets through
-        assert.equal(el.$.pe._propertiesChanged.callCount, 1);
-        assert.equal(el.$.pe._propertiesChanged.firstCall.args[1].obj, nested.obj);
+        // x-pe uses async PropertiesChanged
+        Promise.resolve().then(() => {
+          // Note the PropertiesMixin element only sees a deep set to 'nested.obj.value'
+          // because it overrides _shouldPropertyChange to allow object re-sets through
+          assert.equal(el.$.pe._propertiesChanged.callCount, 1);
+          assert.equal(el.$.pe._propertiesChanged.firstCall.args[1].obj, nested.obj);
+          done();
+        });
         break;
     }
   }
 
-  test('downward data flow', async function() {
+  test('downward data flow', function(done) {
     // Do the thing
     el.nested = {
       obj: {
@@ -152,10 +161,10 @@
       }
     };
     // Verify
-    await verifyObserverOutput(0, el.nested);
+    verifyObserverOutput(0, el.nested, done);
   });
 
-  test('notification from basic element property change', async function() {
+  test('notification from basic element property change', function(done) {
     // Setup
     el.nested = {
       obj: {
@@ -166,10 +175,10 @@
     // Do the thing
     el.$.basic.notifyingValue = 42;
     // Verify
-    await verifyObserverOutput(2, el.nested);
+    verifyObserverOutput(2, el.nested, done);
   });
 
-  test('notification from composed element property change', async function() {
+  test('notification from composed element property change', function(done) {
     // Setup
     el.nested = {
       obj: {
@@ -180,10 +189,10 @@
     // Do the thing
     el.$.compose.$.basic1.notifyingValue = 42;
     // Verify
-    await verifyObserverOutput(2, el.nested);
+    verifyObserverOutput(2, el.nested, done);
   });
 
-  test('notification from forward\'s composed element property change', async function() {
+  test('notification from forward\'s composed element property change', function(done) {
     // Setup
     el.nested = {
       obj: {
@@ -194,10 +203,10 @@
     // Do the thing
     el.$.forward.$.compose.$.basic1.notifyingValue = 42;
     // Verify
-    await verifyObserverOutput(2, el.nested);
+    verifyObserverOutput(2, el.nested, done);
   });
 
-  test('notification from set in top element', async function() {
+  test('notification from set in top element', function(done) {
     // Setup
     el.nested = {
       obj: {
@@ -208,10 +217,10 @@
     // Do the thing
     el.set('nested.obj.value', 42);
     // Verify
-    await verifyObserverOutput(2, el.nested);
+    verifyObserverOutput(2, el.nested, done);
   });
 
-  test('notification from set in composed element', async function() {
+  test('notification from set in composed element', function(done) {
     // Setup
     el.nested = {
       obj: {
@@ -222,10 +231,10 @@
     // Do the thing
     el.$.compose.set('obj.value', 42);
     // Verify
-    await verifyObserverOutput(2, el.nested);
+    verifyObserverOutput(2, el.nested, done);
   });
 
-  test('notification from set in forward element', async function() {
+  test('notification from set in forward element', function(done) {
     // Setup
     el.nested = {
       obj: {
@@ -236,10 +245,10 @@
     // Do the thing
     el.$.forward.set('obj.value', 42);
     // Verify
-    await verifyObserverOutput(2, el.nested);
+    verifyObserverOutput(2, el.nested, done);
   });
 
-  test('notification from set in forward\'s composed element', async function() {
+  test('notification from set in forward\'s composed element', function(done) {
     // Setup
     el.nested = {
       obj: {
@@ -250,10 +259,10 @@
     // Do the thing
     el.$.forward.$.compose.set('obj.value', 42);
     // Verify
-    await verifyObserverOutput(2, el.nested);
+    verifyObserverOutput(2, el.nested, done);
   });
 
-  test('notification from object change in compose element', async function() {
+  test('notification from object change in compose element', function(done) {
     // Setup
     el.nested = {
       obj: {
@@ -266,10 +275,10 @@
       value: 42
     };
     // Verify
-    await verifyObserverOutput(1, el.nested);
+    verifyObserverOutput(1, el.nested, done);
   });
 
-  test('notification from object change in forward element', async function() {
+  test('notification from object change in forward element', function(done) {
     // Setup
     el.nested = {
       obj: {
@@ -282,10 +291,10 @@
       value: 42
     };
     // Verify
-    await verifyObserverOutput(1, el.nested);
+    verifyObserverOutput(1, el.nested, done);
   });
 
-  test('notification from object change in forward\'s compose element', async function() {
+  test('notification from object change in forward\'s compose element', function(done) {
     // Setup
     el.nested = {
       obj: {
@@ -299,7 +308,7 @@
       value: 42
     };
     // Verify
-    await verifyObserverOutput(1, el.nested);
+    verifyObserverOutput(1, el.nested, done);
   });
 
   test('cached paths get invalidated by object sets', function() {