fix: fix getMockedSystemTime for useFakeTimer (#7405)

docs/api/vi.md

@@ -690,7 +690,7 @@ Removes all timers that are scheduled to run. These timers will never run in the
 
 - **Type**: `() => Date | null`
 
-Returns mocked current date that was set using `setSystemTime`. If date is not mocked the method will return `null`.
+Returns mocked current date. If date is not mocked the method will return `null`.
 
 ### vi.getRealSystemTime
 

packages/vitest/src/integrations/mock/timers.ts

@@ -17,8 +17,14 @@ import { mockDate, RealDate, resetDate } from './date'
 export class FakeTimers {
   private _global: typeof globalThis
   private _clock!: InstalledClock
+  // | _fakingTime | _fakingDate |
+  // +-------------+-------------+
+  // | false       | falsy       | initial
+  // | false       | truethy     | vi.setSystemTime called first (for mocking only Date without fake timers)
+  // | true        | falsy       | vi.useFakeTimers called first
+  // | true        | truethy     | unreachable
   private _fakingTime: boolean
-  private _fakingDate: boolean
+  private _fakingDate: Date | null
   private _fakeTimers: FakeTimerWithContext
   private _userConfig?: FakeTimerInstallOpts
   private _now = RealDate.now
@@ -32,7 +38,7 @@ export class FakeTimers {
   }) {
     this._userConfig = config
 
-    this._fakingDate = false
+    this._fakingDate = null
 
     this._fakingTime = false
     this._fakeTimers = withGlobal(global)
@@ -129,7 +135,7 @@ export class FakeTimers {
   useRealTimers(): void {
     if (this._fakingDate) {
       resetDate()
-      this._fakingDate = false
+      this._fakingDate = null
     }
 
     if (this._fakingTime) {
@@ -177,16 +183,21 @@ export class FakeTimers {
     }
   }
 
-  setSystemTime(now?: number | Date): void {
+  setSystemTime(now?: string | number | Date): void {
+    const date = (typeof now === 'undefined' || now instanceof Date) ? now : new Date(now)
     if (this._fakingTime) {
-      this._clock.setSystemTime(now)
+      this._clock.setSystemTime(date)
     }
     else {
-      mockDate(now ?? this.getRealSystemTime())
-      this._fakingDate = true
+      this._fakingDate = date ?? new Date(this.getRealSystemTime())
+      mockDate(this._fakingDate)
     }
   }
 
+  getMockedSystemTime(): Date | null {
+    return this._fakingTime ? new Date(this._clock.now) : this._fakingDate
+  }
+
   getRealSystemTime(): number {
     return this._now()
   }

packages/vitest/src/integrations/vi.ts

@@ -85,7 +85,7 @@ export interface VitestUtils {
    */
   setSystemTime: (time: number | string | Date) => VitestUtils
   /**
-   * Returns mocked current date that was set using `setSystemTime`. If date is not mocked the method will return `null`.
+   * Returns mocked current date. If date is not mocked the method will return `null`.
    */
   getMockedSystemTime: () => Date | null
   /**
@@ -502,14 +502,12 @@ function createVitest(): VitestUtils {
     },
 
     setSystemTime(time: number | string | Date) {
-      const date = time instanceof Date ? time : new Date(time)
-      _mockedDate = date
-      timers().setSystemTime(date)
+      timers().setSystemTime(time)
       return utils
     },
 
     getMockedSystemTime() {
-      return _mockedDate
+      return timers().getMockedSystemTime()
     },
 
     getRealSystemTime() {

test/core/test/timers-getMockedSystemTime.test.ts

@@ -0,0 +1,48 @@
+import { afterEach, expect, it, vi } from 'vitest'
+
+afterEach(() => {
+  vi.useRealTimers()
+})
+
+it('with fake timers', () => {
+  expect(vi.getMockedSystemTime()).toBe(null)
+
+  vi.useFakeTimers()
+  expect(vi.getMockedSystemTime()).toEqual(new Date())
+
+  vi.setSystemTime(0)
+  expect(vi.getMockedSystemTime()).toEqual(new Date())
+  expect(vi.getMockedSystemTime()).toEqual(new Date(0))
+
+  vi.advanceTimersByTime(1234)
+  expect(vi.getMockedSystemTime()).toEqual(new Date())
+  expect(vi.getMockedSystemTime()).toEqual(new Date(1234))
+
+  vi.useRealTimers()
+  expect(vi.getMockedSystemTime()).toBe(null)
+  expect(new Date()).not.toEqual(new Date(1234))
+
+  vi.useFakeTimers({ now: 12345 })
+  expect(vi.getMockedSystemTime()).toEqual(new Date())
+  expect(vi.getMockedSystemTime()).toEqual(new Date(12345))
+})
+
+it('without fake timers', () => {
+  expect(vi.getMockedSystemTime()).toBe(null)
+
+  vi.setSystemTime(0)
+  expect(vi.getMockedSystemTime()).toEqual(new Date())
+  expect(vi.getMockedSystemTime()).toEqual(new Date(0))
+
+  vi.setSystemTime(1234)
+  expect(vi.getMockedSystemTime()).toEqual(new Date())
+  expect(vi.getMockedSystemTime()).toEqual(new Date(1234))
+
+  vi.useRealTimers()
+  expect(vi.getMockedSystemTime()).toBe(null)
+  expect(new Date()).not.toEqual(new Date(1234))
+
+  vi.setSystemTime(12345)
+  expect(vi.getMockedSystemTime()).toEqual(new Date())
+  expect(vi.getMockedSystemTime()).toEqual(new Date(12345))
+})