fix: modern jest timers

Author: thymikee

src/__tests__/auto-cleanup.js

@@ -25,9 +25,22 @@ class Test extends React.Component<*> {
 test('component is mounted, but not umounted before test ends', () => {
   const fn = jest.fn();
   render(<Test onUnmount={fn} />);
+  expect(isMounted).toEqual(true);
   expect(fn).not.toHaveBeenCalled();
 });
 
 test('component is automatically umounted after first test ends', () => {
   expect(isMounted).toEqual(false);
 });
+
+test('does not time out with fake timers', () => {
+  jest.useFakeTimers();
+  render(<Test />);
+  expect(isMounted).toEqual(true);
+});
+
+test('does not time out with modern fake timers', () => {
+  jest.useFakeTimers('modern');
+  render(<Test />);
+  expect(isMounted).toEqual(true);
+});

src/__tests__/waitFor.test.js

@@ -35,6 +35,10 @@ class BananaContainer extends React.Component<{}, any> {
   }
 }
 
+afterEach(() => {
+  jest.useRealTimers();
+});
+
 test('waits for element until it stops throwing', async () => {
   const { getByText, queryByText } = render(<BananaContainer />);
 
@@ -87,9 +91,24 @@ test('works with fake timers', async () => {
   } catch (e) {
     // suppress
   }
-  jest.runTimersToTime(400);
+  jest.advanceTimersByTime(400);
 
   expect(mockFn).toHaveBeenCalledTimes(3);
+});
 
-  jest.useRealTimers();
+test('works with modern fake timers', async () => {
+  jest.useFakeTimers('modern');
+
+  const mockFn = jest.fn(() => {
+    throw Error('test');
+  });
+
+  try {
+    waitFor(() => mockFn(), { timeout: 400, interval: 200 });
+  } catch (e) {
+    // suppress
+  }
+  jest.advanceTimersByTime(400);
+
+  expect(mockFn).toHaveBeenCalledTimes(3);
 });

src/__tests__/waitForElementToBeRemoved.test.js

@@ -25,6 +25,10 @@ const TestSetup = ({ shouldUseDelay = true }) => {
   );
 };
 
+afterEach(() => {
+  jest.useRealTimers();
+});
+
 test('waits when using getBy query', async () => {
   const screen = render(<TestSetup />);
 
@@ -139,3 +143,17 @@ test('works with fake timers', async () => {
   jest.advanceTimersByTime(400);
   expect(mockFn).toHaveBeenCalledTimes(4);
 });
+
+test('works with modern fake timers', async () => {
+  jest.useFakeTimers('modern');
+
+  const mockFn = jest.fn(() => <View />);
+
+  waitForElementToBeRemoved(() => mockFn(), {
+    timeout: 400,
+    interval: 200,
+  });
+
+  jest.advanceTimersByTime(400);
+  expect(mockFn).toHaveBeenCalledTimes(4);
+});

src/flushMicroTasks.js

@@ -2,14 +2,33 @@
 
 import { printDeprecationWarning } from './helpers/errors';
 
+type SimpleThenable = { then: (() => mixed) => mixed };
+
 /**
  * Wait for microtasks queue to flush
  */
-export default function flushMicrotasksQueue(): Promise<any> {
+export default function flushMicrotasksQueue(): SimpleThenable {
   printDeprecationWarning('flushMicrotasksQueue');
   return flushMicroTasks();
 }
 
-export function flushMicroTasks(): Promise<any> {
-  return new Promise((resolve) => setImmediate(resolve));
+let enqueueTask;
+try {
+  // assuming we're in node, let's try to get node's
+  // version of setImmediate, bypassing fake timers if any.
+  // $FlowFixMe - timers is internal Node module
+  enqueueTask = require('timers').setImmediate;
+} catch (_err) {
+  // we're in a browser, do nothing
+  enqueueTask = (resolve) => {
+    resolve();
+  };
+}
+
+export function flushMicroTasks(): SimpleThenable {
+  return {
+    then(resolve) {
+      enqueueTask(resolve);
+    },
+  };
 }