diff --git a/jupyter-js-widgets/src/manager-base.ts b/jupyter-js-widgets/src/manager-base.ts
index aa7643fd10..25ec6e8ff2 100644
--- a/jupyter-js-widgets/src/manager-base.ts
+++ b/jupyter-js-widgets/src/manager-base.ts
@@ -347,16 +347,11 @@ abstract class ManagerBase<T> {
 
     /**
      * Close all widgets and empty the widget state.
-     * @param commlessOnly should only commless widgets be removed
-     * @return promise that resolves when the widget state is cleared.
+     * @return Promise that resolves when the widget state is cleared.
      */
-    clear_state(commlessOnly: boolean): Promise<void> {
+    clear_state(): Promise<void> {
         return utils.resolvePromisesDict(this._models).then((models) => {
-            Object.keys(models).forEach((id) => {
-                if (!commlessOnly || models[id].comm) {
-                    models[id].close();
-                }
-            });
+            Object.keys(models).forEach(id => models[id].close());
             this._models = {};
         });
     };
diff --git a/jupyter-js-widgets/test/src/dummy-manager.ts b/jupyter-js-widgets/test/src/dummy-manager.ts
index 4443ade5f2..ac8b02bf77 100644
--- a/jupyter-js-widgets/test/src/dummy-manager.ts
+++ b/jupyter-js-widgets/test/src/dummy-manager.ts
@@ -15,7 +15,6 @@ class MockComm {
         this.comm_id = `mock-comm-id-${numComms}`;
         numComms += 1;
     }
-    // Somehow the mock comm should trigger a close event?
     on_close(fn) {
         this._on_close = fn;
     };
@@ -24,7 +23,6 @@ class MockComm {
         if (this._on_close) {
             this._on_close();
         }
-        console.error(this._on_close);
     };
     send() {};
     comm_id: string;
diff --git a/jupyter-js-widgets/test/src/manager_test.ts b/jupyter-js-widgets/test/src/manager_test.ts
index 277a8aba90..abdb498e1d 100644
--- a/jupyter-js-widgets/test/src/manager_test.ts
+++ b/jupyter-js-widgets/test/src/manager_test.ts
@@ -149,29 +149,31 @@ describe("ManagerBase", function() {
     });
 
     describe('clear_state', function() {
-      it('exists', function() {
-        expect(this.managerBase.clear_state).to.not.be.undefined;
-      });
-      it('clears the model dictionary', async function() {
+      it('clears the model dictionary and closes widgets', async function() {
         let spec = {
             model_name: 'IntSliderModel',
             model_module: 'jupyter-js-widgets',
             model_module_version: '3.0.0',
         };
-        let mSpec1 = { ...spec, comm: new MockComm()};
-        let mSpec2 = { ...spec, comm: new MockComm()};
+        let comm1 = new MockComm();
+        let comm2 = new MockComm();
+        sinon.spy(comm1, 'close');
+        sinon.spy(comm2, 'close');
+        let mSpec1 = { ...spec, comm: comm1};
+        let mSpec2 = { ...spec, comm: comm2};
         let manager = this.managerBase;
         let model1 = await manager.new_model(mSpec1);
         let model2 = await manager.new_model(mSpec2);
-        let m1 = await manager.get_model(model1.id);
         expect(await manager.get_model(model1.id)).to.be.equal(model1);
         expect(await manager.get_model(model2.id)).to.be.equal(model2);
         await manager.clear_state();
         expect(manager.get_model(model1.id)).to.be.undefined;
         expect(manager.get_model(model2.id)).to.be.undefined;
+        expect((comm1.close as any).calledOnce).to.be.true;
+        expect((comm2.close as any).calledOnce).to.be.true;
+        expect(model1.comm).to.be.undefined;
+        expect(model2.comm).to.be.undefined;
       });
-      it('clears only commless widgets if comlessOnly is true');
-      it('closes the widgets');
     });
 
     describe('get_state', function() {
diff --git a/jupyter-js-widgets/test/src/widget_date_test.ts b/jupyter-js-widgets/test/src/widget_date_test.ts
index 4e739e4fe9..743e8fdfec 100644
--- a/jupyter-js-widgets/test/src/widget_date_test.ts
+++ b/jupyter-js-widgets/test/src/widget_date_test.ts
@@ -48,7 +48,7 @@ describe('DatePickerView', function() {
     });
 
     it('initial date value', function() {
-        const testDate = new Date(2017, 2, 25); // initial date value
+        const testDate = new Date("2017-02-25");
         this.model.set('value', testDate);
         const options = { model: this.model };
         const view = new widgets.DatePickerView(options);
@@ -72,7 +72,7 @@ describe('DatePickerView', function() {
         view.render();
 
         // Simulate setting the date in the datepicker
-        const testDate = new Date(2015, 2, 22);
+        const testDate = new Date("2015-02-22");
         const datepicker = getDatepicker(view.el);
         datepicker.valueAsDate = testDate;
         datepicker.dispatchEvent(new Event('change', {"bubbles":true}));
@@ -87,7 +87,7 @@ describe('DatePickerView', function() {
         const view = new widgets.DatePickerView(options);
         view.render();
 
-        const testDate = new Date(2015, 2, 22);
+        const testDate = new Date("2015-02-22");
         this.model.set('value', testDate);
         const datepicker = getDatepicker(view.el);
         expect(datepicker.valueAsDate.getTime())