In here you have methods to add minutes, hours, days, and years to a date and the unit tests are in the spec file. No need to use external libraries. To use these service just add it to a module then call it.

date-helper.service.spec.ts

import { TestBed } from '@angular/core/testing';

import { configModule } from '../../../../test/test.helper.spec';
import { DateHelperService } from './date-helper.service';

describe('Helper Service', () => {
  let service: DateHelperService;

  const date = new Date(Date.UTC(2019, 0, 9, 12, 25, 2));

  configModule(TestBed, {
    providers: [ DateHelperService ]
  });

  beforeAll(() => {
    service = TestBed.get(DateHelperService);
  });

  it('should be created', () => {
    expect(service).toBeTruthy();
  });

  it('should return current date in milliseconds', () => {
    // GIVEN
    const currentDateInMilliseconds: number = Date.now();
    const currentDateInMillisecondsFromService: number = service.getCurrentDateInMilliseconds();

    // THEN
    expect(currentDateInMillisecondsFromService).toBe(currentDateInMilliseconds);
  });

  it('should convert a date to its value in milliseconds', () => {
    // GIVEN
    const dateInMilliseconds = Date.UTC(2019, 0, 9, 12, 25, 2);
    const dateInMillisecondsFromService: number = service.getDateInMilliseconds(date);

    // THEN
    expect(dateInMillisecondsFromService).toBe(dateInMilliseconds);
  });

  it('should add one minute to the a date', () => {
    // GIVEN
    const datePlusOneMinute = new Date(Date.UTC(2019, 0, 9, 12, 26, 2));
    const datePlusOneMinuteFromService: Date = service.addMinutesToCurrentDate(date, 1);

    // THEN
    expect(datePlusOneMinuteFromService.getTime()).toBe(datePlusOneMinute.getTime());
  });

  it('should add one hour to the a date', () => {
    // GIVEN
    const datePlusOneHour = new Date(Date.UTC(2019, 0, 9, 13, 25, 2));
    const datePlusOneHourFromService: Date = service.addHoursToCurrentDate(date, 1);

    // THEN
    expect(datePlusOneHourFromService.getTime()).toBe(datePlusOneHour.getTime());
  });

  it('should add one day to the a date', () => {
    // GIVEN
    const datePlusOneDay = new Date(Date.UTC(2019, 0, 10, 12, 25, 2));
    const datePlusOneDayFromService: Date = service.addDaysToCurrentDate(date, 1);

    // THEN
    expect(datePlusOneDayFromService.getTime()).toBe(datePlusOneDay.getTime());
  });

  it('should add one year to the a date', () => {
    // GIVEN
    const datePlusOneYear = new Date(Date.UTC(2020, 0, 9, 12, 25, 2));
    const datePlusOneYearFromService: Date = service.addYearsToCurrentDate(date, 1);

    // THEN
    expect(datePlusOneYearFromService.getTime()).toBe(datePlusOneYear.getTime());
  });
});

date-helper.service.ts

import { Injectable } from '@angular/core';

@Injectable()
export class DateHelperService {

  oneMinuteInMilliseconds = 60000;
  oneHourInMinutes = 60;
  oneDayInHours = 24;

  getCurrentDateInMilliseconds() {
    return Date.now();
  }

  getDateInMilliseconds(date) {
    return Date.parse(date);
  }

  addMinutesToCurrentDate(currentDate: Date, extraMinutes: number) {
    const currentDateInMilliseconds = this.getDateInMilliseconds(currentDate);

    const extraMinutesInMilliseconds = extraMinutes
      * this.oneMinuteInMilliseconds;

    const newDate = new Date(currentDateInMilliseconds + extraMinutesInMilliseconds);

    return newDate;
  }

  addHoursToCurrentDate(currentDate: Date, extraHours: number) {
    const currentDateInMilliseconds = this.getDateInMilliseconds(currentDate);

    const extraHoursInMilliseconds = extraHours
      * this.oneHourInMinutes
      * this.oneMinuteInMilliseconds;

    const newDate = new Date(currentDateInMilliseconds + extraHoursInMilliseconds);

    return newDate;
  }

  addDaysToCurrentDate(currentDate: Date, extraDays: number) {
    const currentDateInMilliseconds = this.getDateInMilliseconds(currentDate);

    const extraDaysInMilliseconds = extraDays
      * this.oneDayInHours
      * this.oneHourInMinutes
      * this.oneMinuteInMilliseconds;

    const newDate = new Date(currentDateInMilliseconds + extraDaysInMilliseconds);

    return newDate;
  }

  addYearsToCurrentDate(currentDate: Date, extraYears: number) {
    const currentDateYear = currentDate.getFullYear();
    const currentDateWithExtraYears = currentDate.setFullYear(currentDateYear + extraYears);
    const newDate = new Date(currentDateWithExtraYears);

    return newDate;
  }
}