diff --git a/test/plugin/preParsePostFormat.test.js b/test/plugin/preParsePostFormat.test.js
new file mode 100755
index 000000000..88623496c
--- /dev/null
+++ b/test/plugin/preParsePostFormat.test.js
@@ -0,0 +1,167 @@
+import MockDate from 'mockdate'
+// import moment from 'moment'
+import dayjs from '../../src'
+import preParsePostFormat from '../../src/plugin/preParsePostFormat'
+import duration from '../../src/plugin/duration'
+import calendar from '../../src/plugin/calendar'
+import objectSupport from '../../src/plugin/objectSupport'
+import customParseFormat from '../../src/plugin/customParseFormat'
+import relativeTime from '../../src/plugin/relativeTime'
+import utc from '../../src/plugin/utc'
+import arraySupport from '../../src/plugin/arraySupport'
+import en from '../../src/locale/en'
+
+dayjs.extend(utc)
+dayjs.extend(customParseFormat)
+dayjs.extend(arraySupport)
+dayjs.extend(objectSupport)
+dayjs.extend(calendar)
+dayjs.extend(duration)
+dayjs.extend(relativeTime)
+dayjs.extend(preParsePostFormat)
+
+const symbolMap = {
+  1: '!',
+  2: '@',
+  3: '#',
+  4: '$',
+  5: '%',
+  6: '^',
+  7: '&',
+  8: '*',
+  9: '(',
+  0: ')'
+}
+const numberMap = {
+  '!': '1',
+  '@': '2',
+  '#': '3',
+  $: '4',
+  '%': '5',
+  '^': '6',
+  '&': '7',
+  '*': '8',
+  '(': '9',
+  ')': '0'
+}
+
+const localeCustomizations = {
+  ...en,
+  preparse(string) {
+    if (typeof string !== 'string') {
+      // console.error('preparse - Expected string, got', {
+      //   string
+      // })
+      throw new Error(`preparse - Expected string, got ${typeof string}`)
+    }
+    try {
+      const res = string.replace(/[!@#$%^&*()]/g, match => numberMap[match])
+      // console.log('Called custom preparse', { string, res })
+      return res
+    } catch (error) {
+      const errorMsg = `Unexpected error during preparse of '${string}' - ${error}`
+      // console.error(errorMsg)
+      throw new Error(errorMsg)
+    }
+  },
+  postformat(string) {
+    if (typeof string !== 'string') {
+      // console.error('postformat - Expected string, got', {
+      //   string
+      // })
+      throw new Error(`postformat - Expected string, got ${typeof string}`)
+    }
+    try {
+      const res = string.replace(/\d/g, match => symbolMap[match])
+      // console.log('Called custom postformat', { string, res })
+      return res
+    } catch (error) {
+      const errorMsg = `Unexpected error during postFormat of '${string}' - ${error}`
+      // console.error(errorMsg)
+      throw new Error(errorMsg)
+    }
+  }
+}
+
+beforeEach(() => {
+  MockDate.set(new Date())
+  dayjs.locale('symbol', localeCustomizations)
+})
+
+afterEach(() => {
+  MockDate.reset()
+  dayjs.locale('symbol', null)
+})
+
+describe('preparse and postformat', () => {
+  describe('transform', () => {
+    const TEST_DATE = '@)!@-)*-@&'
+    const TEST_NUM = 1346025600
+    it('preparse string + format', () =>
+      expect(dayjs.utc(TEST_DATE, 'YYYY-MM-DD').unix()).toBe(TEST_NUM))
+    it('preparse ISO8601 string', () =>
+      expect(dayjs.utc(TEST_DATE).unix()).toBe(TEST_NUM))
+    it('postformat', () =>
+      expect(dayjs
+        .unix(TEST_NUM)
+        .utc()
+        .format('YYYY-MM-DD'))
+        .toBe(TEST_DATE))
+  })
+
+  describe('transform from', () => {
+    dayjs.locale('symbol', localeCustomizations)
+    const start = dayjs([2007, 1, 28])
+
+    const t1 = dayjs([2007, 1, 28]).add({ s: 90 })
+    it('postformat should work on dayjs.fn.from', () =>
+      expect(start.from(t1, true)).toBe('@ minutes'))
+
+    const t2 = dayjs().add(6, 'd')
+    it('postformat should work on dayjs.fn.fromNow', () =>
+      expect(t2.fromNow(true)).toBe('^ days'))
+
+    it('postformat should work on dayjs.duration.fn.humanize', () =>
+      expect(dayjs.duration(10, 'h').humanize()).toBe('!) hours'))
+  })
+})
+
+describe('calendar day', () => {
+  const a = dayjs()
+    .hour(12)
+    .minute(0)
+    .second(0)
+
+  it('today at the same time', () =>
+    expect(dayjs(a).calendar()).toBe('Today at !@:)) PM'))
+
+  it('Now plus 25 min', () =>
+    expect(dayjs(a)
+      .add({ m: 25 })
+      .calendar())
+      .toBe('Today at !@:@% PM'))
+
+  it('Now plus 1 hour', () =>
+    expect(dayjs(a)
+      .add({ h: 1 })
+      .calendar())
+      .toBe('Today at !:)) PM'))
+
+  it('tomorrow at the same time', () =>
+    expect(dayjs(a)
+      .add({ d: 1 })
+      .calendar())
+      .toBe('Tomorrow at !@:)) PM'))
+
+  it('Now minus 1 hour', () =>
+    expect(dayjs(a)
+      .subtract({ h: 1 })
+      .calendar())
+      .toBe('Today at !!:)) AM'))
+
+  it('yesterday at the same time', () =>
+    expect(dayjs(a)
+      .subtract({ d: 1 })
+      .calendar())
+      .toBe('Yesterday at !@:)) PM'))
+})