fix: Fix UTC plugin add day DST bug

package.json

@@ -6,8 +6,8 @@
   "types": "index.d.ts",
   "module": "dayjs.min.js",
   "scripts": {
-    "test": "TZ=Pacific/Auckland npm run test-tz && TZ=Europe/London npm run test-tz && npm run test-tz && jest",
-    "test-tz": "jest test/timezone.test --coverage=false",
+    "test": "TZ=Pacific/Auckland npm run test-tz && TZ=Europe/London npm run test-tz && TZ=America/Whitehorse npm run test-tz && npm run test-tz && jest",
+    "test-tz": "date && jest test/timezone.test --coverage=false",
     "lint": "./node_modules/.bin/eslint src/* test/* build/*",
     "prettier": "prettier --write \"docs/**/*.md\"",
     "babel": "cross-env BABEL_ENV=build babel src --out-dir esm --copy-files && node build/esm",

src/index.js

@@ -242,9 +242,8 @@ class Dayjs {
     number = Number(number) // eslint-disable-line no-param-reassign
     const unit = Utils.p(units)
     const instanceFactorySet = (n) => {
-      const date = new Date(this.$d)
-      date.setDate(date.getDate() + Math.round(n * number))
-      return Utils.w(date, this)
+      const d = dayjs(this)
+      return Utils.w(d.date(d.date() + Math.round(n * number)), this)
     }
     if (unit === C.M) {
       return this.set(C.M, this.$M + number)

test/display.test.js

@@ -98,6 +98,12 @@ it('Format Minute m mm', () => {
 })
 
 it('Format Second s ss SSS', () => {
+  // Todo: debug CI error
+  console.log(Date.now()) // eslint-disable-line no-console
+  console.log((new Date()).toString()) // eslint-disable-line no-console
+  console.log((new Date()).toLocaleString()) // eslint-disable-line no-console
+  console.log((new Date()).getTimezoneOffset()) // eslint-disable-line no-console
+  // debug
   expect(dayjs().format('s')).toBe(moment().format('s'))
   expect(dayjs().format('ss')).toBe(moment().format('ss'))
   expect(dayjs().format('SSS')).toBe(moment().format('SSS'))

test/timezone.test.js

@@ -1,6 +1,9 @@
 import moment from 'moment'
 import MockDate from 'mockdate'
 import dayjs from '../src'
+import utc from '../src/plugin/utc'
+
+dayjs.extend(utc)
 
 beforeEach(() => {
   MockDate.set(new Date())
@@ -36,3 +39,18 @@ it('Diff (DST)', () => {
     expect(dayjsA.diff(dayjsB, unit, true)).toBe(momentA.diff(momentB, unit, true))
   })
 })
+
+it('UTC add day in DST', () => {
+  const testDate = '2019-03-10'
+  const dayTest = dayjs(testDate)
+    .utc()
+    .startOf('day')
+  const momentTest = moment(testDate)
+    .utc()
+    .startOf('day')
+  expect(dayTest.add(1, 'day').format())
+    .toBe(momentTest.clone().add(1, 'day').format())
+  expect(dayTest.add(2, 'day').format())
+    .toBe(momentTest.clone().add(2, 'day').format())
+})
+