Adjust tests to not assume the callbacks argument will be modified.

Author: jasongrout

packages/base/test/src/widget_test.ts

@@ -643,7 +643,7 @@ describe('WidgetModel', function () {
       });
       expect(this.widget._msg_buffer_callbacks).to.not.equals(null);
       // have the comm send a status idle message
-      callbacks.iopub.status({
+      this.comm.send.lastCall.args[1].iopub.status({
         content: {
           execution_state: 'idle',
         },
@@ -662,7 +662,7 @@ describe('WidgetModel', function () {
         },
         buffer_paths: [],
       });
-      callbacks.iopub.status({
+      this.comm.send.lastCall.args[1].iopub.status({
         content: {
           execution_state: 'idle',
         },
@@ -687,7 +687,7 @@ describe('WidgetModel', function () {
         state: { a: 'sync test - 2' },
         buffer_paths: [],
       });
-      callbacks.iopub.status({
+      this.comm.send.lastCall.args[1].iopub.status({
         content: {
           execution_state: 'idle',
         },
@@ -703,7 +703,7 @@ describe('WidgetModel', function () {
         },
         buffer_paths: [],
       });
-      callbacks.iopub.status({
+      this.comm.send.lastCall.args[1].iopub.status({
         content: {
           execution_state: 'idle',
         },