act should work without mock Scheduler

packages/react-dom/src/__tests__/ReactTestUtilsActUnmockedScheduler-test.js

@@ -47,6 +47,7 @@ afterEach(() => {
   document.body.removeChild(container);
 });
 
+// @gate __DEV__
 it('can use act to flush effects', () => {
   function App() {
     React.useEffect(() => {
@@ -62,6 +63,7 @@ it('can use act to flush effects', () => {
   expect(clearYields()).toEqual([100]);
 });
 
+// @gate __DEV__
 it('flushes effects on every call', () => {
   function App() {
     const [ctr, setCtr] = React.useState(0);
@@ -100,6 +102,7 @@ it('flushes effects on every call', () => {
   expect(button.innerHTML).toEqual('5');
 });
 
+// @gate __DEV__
 it("should keep flushing effects until they're done", () => {
   function App() {
     const [ctr, setCtr] = React.useState(0);
@@ -118,6 +121,7 @@ it("should keep flushing effects until they're done", () => {
   expect(container.innerHTML).toEqual('5');
 });
 
+// @gate __DEV__
 it('should flush effects only on exiting the outermost act', () => {
   function App() {
     React.useEffect(() => {
@@ -138,6 +142,7 @@ it('should flush effects only on exiting the outermost act', () => {
   expect(clearYields()).toEqual([0]);
 });
 
+// @gate __DEV__
 it('can handle cascading promises', async () => {
   // this component triggers an effect, that waits a tick,
   // then sets state. repeats this 5 times.

packages/react-dom/src/__tests__/ReactUnmockedSchedulerWarning-test.js

@@ -7,56 +7,142 @@
  * @emails react-core
  */
 
-let React;
-let ReactDOM;
-
-function App() {
-  return null;
-}
-
 beforeEach(() => {
   jest.resetModules();
-  jest.unmock('scheduler');
-  React = require('react');
-  ReactDOM = require('react-dom');
+
+  // Unmock the Scheduler, which is mocked by default in our test setup
+  jest.mock('scheduler', () => require.requireActual('scheduler'));
+  jest.mock('scheduler/src/SchedulerHostConfig', () =>
+    require.requireActual('scheduler/src/forks/SchedulerHostConfig.default.js'),
+  );
+});
+
+// @gate __DEV__
+it('public implementation of `act` works without mocking scheduler (DOM)', async () => {
+  const React = require('react');
+  const ReactDOM = require('react-dom');
+  const TestUtils = require('react-dom/test-utils');
+
+  const log = [];
+
+  function App() {
+    React.useEffect(() => {
+      log.push('Did mount');
+    }, []);
+    return 'App';
+  }
+
+  const container = document.createElement('div');
+  await TestUtils.act(async () => {
+    ReactDOM.render(<App />, container);
+  });
+  expect(container.textContent).toEqual('App');
+  expect(log).toEqual(['Did mount']);
 });
 
-it('does not warn when rendering in legacy mode', () => {
-  expect(() => {
-    ReactDOM.render(<App />, document.createElement('div'));
-  }).toErrorDev([]);
+it('internal implementation of `act` throws if Scheduler is not mocked (DOM)', async () => {
+  const React = require('react');
+  const ReactDOM = require('react-dom');
+  const TestUtils = require('react-dom/test-utils');
+
+  const log = [];
+
+  function App() {
+    React.useEffect(() => {
+      log.push('Did mount');
+    }, []);
+    return 'App';
+  }
+
+  const container = document.createElement('div');
+  let error = null;
+  try {
+    await TestUtils.unstable_concurrentAct(async () => {
+      ReactDOM.render(<App />, container);
+    });
+  } catch (e) {
+    error = e;
+  }
+  expect(error).not.toBe(null);
+  expect(error.message).toEqual(
+    'This version of `act` requires a special mock build of Scheduler.',
+  );
 });
 
-// @gate experimental
-it('should warn when rendering in concurrent mode', () => {
-  expect(() => {
-    ReactDOM.unstable_createRoot(document.createElement('div')).render(<App />);
-  }).toErrorDev(
-    'In Concurrent or Sync modes, the "scheduler" module needs to be mocked ' +
-      'to guarantee consistent behaviour across tests and browsers.',
-    {withoutStack: true},
+it('internal implementation of `act` throws if Scheduler is not mocked (noop)', async () => {
+  const React = require('react');
+  const ReactNoop = require('react-noop-renderer');
+
+  const log = [];
+
+  function App() {
+    React.useEffect(() => {
+      log.push('Did mount');
+    }, []);
+    return 'App';
+  }
+
+  const root = ReactNoop.createRoot();
+  let error = null;
+  try {
+    await ReactNoop.act(async () => {
+      root.render(<App />);
+    });
+  } catch (e) {
+    error = e;
+  }
+  expect(error).not.toBe(null);
+  expect(error.message).toEqual(
+    'This version of `act` requires a special mock build of Scheduler.',
   );
-  // does not warn twice
-  expect(() => {
-    ReactDOM.unstable_createRoot(document.createElement('div')).render(<App />);
-  }).toErrorDev([]);
 });
 
-// @gate experimental
-it('should warn when rendering in blocking mode', () => {
-  expect(() => {
-    ReactDOM.unstable_createBlockingRoot(document.createElement('div')).render(
-      <App />,
-    );
-  }).toErrorDev(
-    'In Concurrent or Sync modes, the "scheduler" module needs to be mocked ' +
-      'to guarantee consistent behaviour across tests and browsers.',
-    {withoutStack: true},
+// @gate __DEV__
+it('public implementation of `act` works without mocking scheduler (test renderer)', async () => {
+  const React = require('react');
+  const ReactTestRenderer = require('react-test-renderer');
+
+  const log = [];
+
+  function App() {
+    React.useEffect(() => {
+      log.push('Did mount');
+    }, []);
+    return 'App';
+  }
+
+  const root = ReactTestRenderer.create(null);
+  await ReactTestRenderer.act(async () => {
+    root.update(<App />);
+  });
+  expect(root.toJSON()).toEqual('App');
+  expect(log).toEqual(['Did mount']);
+});
+
+it('internal implementation of `act` throws if Scheduler is not mocked (test renderer)', async () => {
+  const React = require('react');
+  const ReactTestRenderer = require('react-test-renderer');
+
+  const log = [];
+
+  function App() {
+    React.useEffect(() => {
+      log.push('Did mount');
+    }, []);
+    return 'App';
+  }
+
+  const root = ReactTestRenderer.create(null);
+  let error = null;
+  try {
+    await ReactTestRenderer.unstable_concurrentAct(async () => {
+      root.update(<App />);
+    });
+  } catch (e) {
+    error = e;
+  }
+  expect(error).not.toBe(null);
+  expect(error.message).toEqual(
+    'This version of `act` requires a special mock build of Scheduler.',
   );
-  // does not warn twice
-  expect(() => {
-    ReactDOM.unstable_createBlockingRoot(document.createElement('div')).render(
-      <App />,
-    );
-  }).toErrorDev([]);
 });

packages/react-reconciler/src/ReactFiberReconciler.new.js

@@ -61,7 +61,6 @@ import {
   flushDiscreteUpdates,
   flushPassiveEffects,
   warnIfNotScopedWithMatchingAct,
-  warnIfUnmockedScheduler,
   IsThisRendererActing,
   act,
 } from './ReactFiberWorkLoop.new';
@@ -261,7 +260,6 @@ export function updateContainer(
   if (__DEV__) {
     // $FlowExpectedError - jest isn't a global, and isn't recognized outside of tests
     if ('undefined' !== typeof jest) {
-      warnIfUnmockedScheduler(current);
       warnIfNotScopedWithMatchingAct(current);
     }
   }

packages/react-reconciler/src/ReactFiberReconciler.old.js

@@ -61,7 +61,6 @@ import {
   flushDiscreteUpdates,
   flushPassiveEffects,
   warnIfNotScopedWithMatchingAct,
-  warnIfUnmockedScheduler,
   IsThisRendererActing,
   act,
 } from './ReactFiberWorkLoop.old';
@@ -261,7 +260,6 @@ export function updateContainer(
   if (__DEV__) {
     // $FlowExpectedError - jest isn't a global, and isn't recognized outside of tests
     if ('undefined' !== typeof jest) {
-      warnIfUnmockedScheduler(current);
       warnIfNotScopedWithMatchingAct(current);
     }
   }