test to show changes with modern timer mocks

Author: mikeduminy

src/__tests__/timerUtils.js

@@ -1,3 +1,5 @@
+import { setTimeout } from '../helpers/getTimerFuncs';
+
 const FakeTimerTypes = [
   'default',
   'legacy',
@@ -18,4 +20,8 @@ function setupFakeTimers(fakeTimerType) {
   }
 }
 
-export { FakeTimerTypes, setupFakeTimers };
+async function sleep(ms) {
+  return new Promise((resolve) => setTimeout(resolve, ms));
+}
+
+export { FakeTimerTypes, setupFakeTimers, sleep };

src/__tests__/waitFor.test.js

@@ -1,8 +1,8 @@
 // @flow
 import * as React from 'react';
-import { View, Text, TouchableOpacity } from 'react-native';
-import { render, fireEvent, waitFor } from '..';
-import { FakeTimerTypes, setupFakeTimers } from './timerUtils';
+import { Text, TouchableOpacity, View } from 'react-native';
+import { fireEvent, render, waitFor } from '..';
+import { FakeTimerTypes, setupFakeTimers, sleep } from './timerUtils';
 
 class Banana extends React.Component<any> {
   changeFresh = () => {
@@ -137,3 +137,30 @@ test.each(FakeTimerTypes)(
     expect(mockFn).toHaveBeenCalledTimes(3);
   }
 );
+
+// this test leads to a console error: Warning: You called act(async () => ...) without await, but does not fail the test
+// it is included to show that the previous approach of faking modern timers still works
+// the gotcha is that the try catch will fail to catch the final error, which is why we need to stop throwing
+test('non-awaited approach is not affected by fake modern timers', async () => {
+  jest.useFakeTimers('modern');
+
+  let calls = 0;
+  const mockFn = jest.fn(() => {
+    calls += 1;
+    if (calls < 3) {
+      throw Error('test');
+    }
+  });
+
+  try {
+    waitFor(() => mockFn(), { timeout: 400, interval: 200 });
+  } catch (e) {
+    // suppress
+  }
+  jest.advanceTimersByTime(400);
+  expect(mockFn).toHaveBeenCalledTimes(0);
+
+  jest.useRealTimers();
+  await sleep(500);
+  expect(mockFn).toHaveBeenCalledTimes(3);
+});

src/helpers/getTimerFuncs.js

@@ -21,7 +21,6 @@ function runWithRealTimers(callback) {
 }
 
 function getJestFakeTimersType() {
-  // istanbul ignore if
   if (
     typeof jest === 'undefined' ||
     typeof globalObj.setTimeout === 'undefined'
@@ -52,13 +51,11 @@ function getJestFakeTimersType() {
 }
 
 // we only run our tests in node, and setImmediate is supported in node.
-// istanbul ignore next
 function setImmediatePolyfill(fn) {
   return globalObj.setTimeout(fn, 0);
 }
 
 function getTimeFunctions() {
-  // istanbul ignore next
   return {
     clearTimeoutFn: globalObj.clearTimeout,
     setImmediateFn: globalObj.setImmediate || setImmediatePolyfill,