tests (calendar): fix import issue

Author: Tobias Schweizer

src/lib/datepicker/calendar.spec.ts

@@ -5,7 +5,7 @@ import {
 import {dispatchFakeEvent, dispatchKeyboardEvent, dispatchMouseEvent} from '@angular/cdk/testing';
 import {Component} from '@angular/core';
 import {ComponentFixture, TestBed, async, inject} from '@angular/core/testing';
-import {DEC, FEB, JAN, NOV} from '@angular/material/core';
+import {DEC, FEB, JAN, MatNativeDateModule, NOV} from '@angular/material/core';
 import {By} from '@angular/platform-browser';
 import {Direction, Directionality} from '@angular/cdk/bidi';
 import {MatCalendar} from './calendar';
@@ -15,14 +15,18 @@ import {MatMonthView} from './month-view';
 import {MatMultiYearView, yearsPerPage} from './multi-year-view';
 import {MatYearView} from './year-view';
 import {MatDatepickerModule} from './datepicker-module';
+import {PortalModule} from '@angular/cdk/portal';
+import {MatButtonModule} from '@angular/material/button';
 
 describe('MatCalendar', () => {
   let dir: {value: Direction};
 
   beforeEach(async(() => {
     TestBed.configureTestingModule({
       imports: [
-        MatDatepickerModule,
+          MatButtonModule,
+          MatNativeDateModule,
+          PortalModule,
       ],
       declarations: [
         MatCalendar,