Vue.js/test/unit/features/instance/methods-watch.spec.js

import Vue from 'vue'

describe('Instance methods watch', () => {
  let vm, spy
  beforeEach(() => {
    vm = new Vue({
      data: {
        a: {
          b: 1
        }
      }
    })
    spy = jasmine.createSpy('watch')
  })

  it('basic usage', done => {
    vm.$watch('a.b', spy)
    vm.a.b = 2
    waitForUpdate(() => {
      expect(spy.calls.count()).toBe(1)
      expect(spy).toHaveBeenCalledWith(2, 1)
      vm.a = { b: 3 }
    }).then(() => {
      expect(spy.calls.count()).toBe(2)
      expect(spy).toHaveBeenCalledWith(3, 2)
    }).then(done)
  })

  it('immediate', () => {
    vm.$watch('a.b', spy, { immediate: true })
    expect(spy.calls.count()).toBe(1)
    expect(spy).toHaveBeenCalledWith(1)
  })

  it('unwatch', done => {
    const unwatch = vm.$watch('a.b', spy)
    unwatch()
    vm.a.b = 2
    waitForUpdate(() => {
      expect(spy.calls.count()).toBe(0)
    }).then(done)
  })

  it('function watch', done => {
    vm.$watch(function () {
      return this.a.b
    }, spy)
    vm.a.b = 2
    waitForUpdate(() => {
      expect(spy).toHaveBeenCalledWith(2, 1)
    }).then(done)
  })

  it('deep watch', done => {
    var oldA = vm.a
    vm.$watch('a', spy, { deep: true })
    vm.a.b = 2
    waitForUpdate(() => {
      expect(spy).toHaveBeenCalledWith(oldA, oldA)
      vm.a = { b: 3 }
    }).then(() => {
      expect(spy).toHaveBeenCalledWith(vm.a, oldA)
    }).then(done)
  })

  it('warn expresssion', () => {
    vm.$watch('a + b', spy)
    expect('Watcher only accepts simple dot-delimited paths').toHaveBeenWarned()
  })
})