docs(fakeTimers): Explain how to use fake timers in testing-library

docs/using-fake-timers.md

@@ -0,0 +1,34 @@
+---
+id: using-fake-timers
+title: Using Fake Timers
+sidebar_label: Using Fake Timers
+---
+
+Using real timers in your tests is less common since they depend on real time
+lapse. To solve this, most testing frameworks offer the option to use fake
+timers in your tests so you won't need to rely on real times.
+
+When using fake timers in your tests, all of the code inside your test uses fake
+timers. The common pattern to setup fake timers is usually within the
+`beforeEach`, here's an example of how to do that using jest:
+
+```js
+beforeEach(() => {
+  jest.useFakeTimers()
+})
+```
+
+When doing so, you'll probably want to restore the timers after your test runs.
+For that you usually call `useRealTimers` in `afterEach`. It's important to
+remember that before calling `useRealTimers` you should call
+`runOnlyPendingTimers`. This will ensure you progress all pending timers so none
+of them are left hanging and don't get executed.  
+That way, your fake timers are encapsulated to your tests only and all of them
+behave as you would expect. Here's an example of doing that using jest:
+
+```js
+afterEach(() => {
+  jest.runOnlyPendingTimers()
+  jest.useRealTimers()
+})
+```

website/sidebars.json

@@ -1,6 +1,6 @@
 {
   "docs": {
-    "Getting Started": ["intro", "guiding-principles"],
+    "Getting Started": ["intro", "guiding-principles", "using-fake-timers"],
     "Frameworks": [
       {
         "type": "subcategory",