update docs

CHANGELOG.md

@@ -25,6 +25,7 @@
 - `[babel-preset-jest]` [**BREAKING**] Export a function instead of an object for Babel 7 compatibility ([#7203](https://github.com/facebook/jest/pull/7203))
 - `[expect]` Check constructor equality in .toStrictEqual() ([#7005](https://github.com/facebook/jest/pull/7005))
 - `[jest-util]` Add `jest.getTimerCount()` to get the count of scheduled fake timers ([#7285](https://github.com/facebook/jest/pull/7285))
+- `[jest-util]`[**BREAKING**] Replace Jest's fake timers implementation with Lolex ([#5171](https://github.com/facebook/jest/pull/5171))
 
 ### Fixes
 

docs/JestObjectAPI.md

@@ -447,6 +447,14 @@ This means, if any timers have been scheduled (but have not yet executed), they
 
 Returns the number of fake timers still left to run.
 
+### `.jest.setSystemTime()`
+
+Set the current system time used by fake timers. Simulates a user changing the system clock while your program is running. It affects the current time but it does not in itself cause e.g. timers to fire; they will fire exactly as they would have done without the call to `jest.setSystemTime()`.
+
+### `.jest.getRealSystemTime()`
+
+When mocking time, `Date.now()` will also be mocked. If you for some reason need access to the real current time, you can invoke this function.
+
 ## Misc
 
 ### `jest.setTimeout(timeout)`

packages/jest-util/src/__tests__/fake_timers.test.js

@@ -491,7 +491,7 @@ describe('FakeTimers', () => {
       });
 
       timers.runOnlyPendingTimers();
-      expect(runOrder).toEqual([
+      const firsRunOrder = [
         'mock4',
         'mock5',
         'mock2',
@@ -502,20 +502,13 @@ describe('FakeTimers', () => {
         'mock3',
         'mock1',
         'mock2',
-      ]);
+      ];
+
+      expect(runOrder).toEqual(firsRunOrder);
 
       timers.runOnlyPendingTimers();
       expect(runOrder).toEqual([
-        'mock4',
-        'mock5',
-        'mock2',
-        'mock2',
-        'mock1',
-        'mock2',
-        'mock2',
-        'mock3',
-        'mock1',
-        'mock2',
+        ...firsRunOrder,
         'mock2',
         'mock1',
         'mock2',