Add tests for non-React discrete events flushing in a microtask (#20772)

* Convert some old discrete tests to Hooks

I'm planning to copy paste so why not update them anyway.

* Copy paste discrete tests into another file

These are still using React events. I'll change that next.

* Convert the test to use native events

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

@@ -148,13 +148,6 @@ describe('ReactDOMFiberAsync', () => {
   });
 
   describe('concurrent mode', () => {
-    beforeEach(() => {
-      jest.resetModules();
-
-      ReactDOM = require('react-dom');
-      Scheduler = require('scheduler');
-    });
-
     // @gate experimental
     it('does not perform deferred updates synchronously', () => {
       const inputRef = React.createRef();
@@ -399,28 +392,26 @@ describe('ReactDOMFiberAsync', () => {
 
       let formSubmitted = false;
 
-      class Form extends React.Component {
-        state = {active: true};
-        disableForm = () => {
-          this.setState({active: false});
-        };
-        submitForm = () => {
+      function Form() {
+        const [active, setActive] = React.useState(true);
+        function disableForm() {
+          setActive(false);
+        }
+        function submitForm() {
           formSubmitted = true; // This should not get invoked
-        };
-        render() {
-          return (
-            <div>
-              <button onClick={this.disableForm} ref={disableButtonRef}>
-                Disable
-              </button>
-              {this.state.active ? (
-                <button onClick={this.submitForm} ref={submitButtonRef}>
-                  Submit
-                </button>
-              ) : null}
-            </div>
-          );
         }
+        return (
+          <div>
+            <button onClick={disableForm} ref={disableButtonRef}>
+              Disable
+            </button>
+            {active ? (
+              <button onClick={submitForm} ref={submitButtonRef}>
+                Submit
+              </button>
+            ) : null}
+          </div>
+        );
       }
 
       const root = ReactDOM.unstable_createRoot(container);
@@ -461,33 +452,29 @@ describe('ReactDOMFiberAsync', () => {
 
       let formSubmitted = false;
 
-      class Form extends React.Component {
-        state = {active: true};
-        disableForm = () => {
-          this.setState({active: false});
-        };
-        submitForm = () => {
+      function Form() {
+        const [active, setActive] = React.useState(true);
+        function disableForm() {
+          setActive(false);
+        }
+        function submitForm() {
           formSubmitted = true; // This should not get invoked
-        };
-        disabledSubmitForm = () => {
+        }
+        function disabledSubmitForm() {
           // The form is disabled.
-        };
-        render() {
-          return (
-            <div>
-              <button onClick={this.disableForm} ref={disableButtonRef}>
-                Disable
-              </button>
-              <button
-                onClick={
-                  this.state.active ? this.submitForm : this.disabledSubmitForm
-                }
-                ref={submitButtonRef}>
-                Submit
-              </button>
-            </div>
-          );
         }
+        return (
+          <div>
+            <button onClick={disableForm} ref={disableButtonRef}>
+              Disable
+            </button>
+            <button
+              onClick={active ? submitForm : disabledSubmitForm}
+              ref={submitButtonRef}>
+              Submit
+            </button>
+          </div>
+        );
       }
 
       const root = ReactDOM.unstable_createRoot(container);
@@ -526,29 +513,24 @@ describe('ReactDOMFiberAsync', () => {
 
       let formSubmitted = false;
 
-      class Form extends React.Component {
-        state = {active: false};
-        enableForm = () => {
-          this.setState({active: true});
-        };
-        submitForm = () => {
-          formSubmitted = true; // This should happen
-        };
-        render() {
-          return (
-            <div>
-              <button onClick={this.enableForm} ref={enableButtonRef}>
-                Enable
-              </button>
-              <button
-                onClick={this.state.active ? this.submitForm : null}
-                ref={submitButtonRef}>
-                Submit
-              </button>{' '}
-              : null}
-            </div>
-          );
+      function Form() {
+        const [active, setActive] = React.useState(false);
+        function enableForm() {
+          setActive(true);
+        }
+        function submitForm() {
+          formSubmitted = true; // This should not get invoked
         }
+        return (
+          <div>
+            <button onClick={enableForm} ref={enableButtonRef}>
+              Enable
+            </button>
+            <button onClick={active ? submitForm : null} ref={submitButtonRef}>
+              Submit
+            </button>
+          </div>
+        );
       }
 
       const root = ReactDOM.unstable_createRoot(container);

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

@@ -0,0 +1,228 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @emails react-core
+ */
+
+'use strict';
+
+let React;
+
+let ReactDOM;
+let Scheduler;
+
+describe('ReactDOMNativeEventHeuristic-test', () => {
+  let container;
+
+  beforeEach(() => {
+    jest.resetModules();
+    container = document.createElement('div');
+    React = require('react');
+    ReactDOM = require('react-dom');
+    Scheduler = require('scheduler');
+
+    document.body.appendChild(container);
+  });
+
+  afterEach(() => {
+    document.body.removeChild(container);
+  });
+
+  function dispatchAndSetCurrentEvent(el, event) {
+    try {
+      window.event = event;
+      el.dispatchEvent(event);
+    } finally {
+      window.event = undefined;
+    }
+  }
+
+  // @gate experimental
+  // @gate enableDiscreteEventMicroTasks && enableNativeEventPriorityInference
+  it('ignores discrete events on a pending removed element', async () => {
+    const disableButtonRef = React.createRef();
+    const submitButtonRef = React.createRef();
+
+    function Form() {
+      const [active, setActive] = React.useState(true);
+
+      React.useLayoutEffect(() => {
+        disableButtonRef.current.onclick = disableForm;
+      });
+
+      function disableForm() {
+        setActive(false);
+      }
+
+      return (
+        <div>
+          <button ref={disableButtonRef}>Disable</button>
+          {active ? <button ref={submitButtonRef}>Submit</button> : null}
+        </div>
+      );
+    }
+
+    const root = ReactDOM.unstable_createRoot(container);
+    root.render(<Form />);
+    // Flush
+    Scheduler.unstable_flushAll();
+
+    const disableButton = disableButtonRef.current;
+    expect(disableButton.tagName).toBe('BUTTON');
+
+    // Dispatch a click event on the Disable-button.
+    const firstEvent = document.createEvent('Event');
+    firstEvent.initEvent('click', true, true);
+    expect(() =>
+      dispatchAndSetCurrentEvent(disableButton, firstEvent),
+    ).toErrorDev(['An update to Form inside a test was not wrapped in act']);
+
+    // There should now be a pending update to disable the form.
+    // This should not have flushed yet since it's in concurrent mode.
+    const submitButton = submitButtonRef.current;
+    expect(submitButton.tagName).toBe('BUTTON');
+
+    // Discrete events should be flushed in a microtask.
+    // Verify that the second button was removed.
+    await null;
+    expect(submitButtonRef.current).toBe(null);
+    // We'll assume that the browser won't let the user click it.
+  });
+
+  // @gate experimental
+  // @gate enableDiscreteEventMicroTasks && enableNativeEventPriorityInference
+  it('ignores discrete events on a pending removed event listener', async () => {
+    const disableButtonRef = React.createRef();
+    const submitButtonRef = React.createRef();
+
+    let formSubmitted = false;
+
+    function Form() {
+      const [active, setActive] = React.useState(true);
+
+      React.useLayoutEffect(() => {
+        disableButtonRef.current.onclick = disableForm;
+        submitButtonRef.current.onclick = active
+          ? submitForm
+          : disabledSubmitForm;
+      });
+
+      function disableForm() {
+        setActive(false);
+      }
+
+      function submitForm() {
+        formSubmitted = true; // This should not get invoked
+      }
+
+      function disabledSubmitForm() {
+        // The form is disabled.
+      }
+
+      return (
+        <div>
+          <button ref={disableButtonRef}>Disable</button>
+          <button ref={submitButtonRef}>Submit</button>
+        </div>
+      );
+    }
+
+    const root = ReactDOM.unstable_createRoot(container);
+    root.render(<Form />);
+    // Flush
+    Scheduler.unstable_flushAll();
+
+    const disableButton = disableButtonRef.current;
+    expect(disableButton.tagName).toBe('BUTTON');
+
+    // Dispatch a click event on the Disable-button.
+    const firstEvent = document.createEvent('Event');
+    firstEvent.initEvent('click', true, true);
+    expect(() => {
+      dispatchAndSetCurrentEvent(disableButton, firstEvent);
+    }).toErrorDev(['An update to Form inside a test was not wrapped in act']);
+
+    // There should now be a pending update to disable the form.
+    // This should not have flushed yet since it's in concurrent mode.
+    const submitButton = submitButtonRef.current;
+    expect(submitButton.tagName).toBe('BUTTON');
+
+    // Discrete events should be flushed in a microtask.
+    await null;
+
+    // Now let's dispatch an event on the submit button.
+    const secondEvent = document.createEvent('Event');
+    secondEvent.initEvent('click', true, true);
+    dispatchAndSetCurrentEvent(submitButton, secondEvent);
+
+    // Therefore the form should never have been submitted.
+    expect(formSubmitted).toBe(false);
+  });
+
+  // @gate experimental
+  // @gate enableDiscreteEventMicroTasks && enableNativeEventPriorityInference
+  it('uses the newest discrete events on a pending changed event listener', async () => {
+    const enableButtonRef = React.createRef();
+    const submitButtonRef = React.createRef();
+
+    let formSubmitted = false;
+
+    function Form() {
+      const [active, setActive] = React.useState(false);
+
+      React.useLayoutEffect(() => {
+        enableButtonRef.current.onclick = enableForm;
+        submitButtonRef.current.onclick = active ? submitForm : null;
+      });
+
+      function enableForm() {
+        setActive(true);
+      }
+
+      function submitForm() {
+        formSubmitted = true; // This should not get invoked
+      }
+
+      return (
+        <div>
+          <button ref={enableButtonRef}>Enable</button>
+          <button ref={submitButtonRef}>Submit</button>
+        </div>
+      );
+    }
+
+    const root = ReactDOM.unstable_createRoot(container);
+    root.render(<Form />);
+    // Flush
+    Scheduler.unstable_flushAll();
+
+    const enableButton = enableButtonRef.current;
+    expect(enableButton.tagName).toBe('BUTTON');
+
+    // Dispatch a click event on the Enable-button.
+    const firstEvent = document.createEvent('Event');
+    firstEvent.initEvent('click', true, true);
+    expect(() => {
+      dispatchAndSetCurrentEvent(enableButton, firstEvent);
+    }).toErrorDev(['An update to Form inside a test was not wrapped in act']);
+
+    // There should now be a pending update to enable the form.
+    // This should not have flushed yet since it's in concurrent mode.
+    const submitButton = submitButtonRef.current;
+    expect(submitButton.tagName).toBe('BUTTON');
+
+    // Discrete events should be flushed in a microtask.
+    await null;
+
+    // Now let's dispatch an event on the submit button.
+    const secondEvent = document.createEvent('Event');
+    secondEvent.initEvent('click', true, true);
+    dispatchAndSetCurrentEvent(submitButton, secondEvent);
+
+    // Therefore the form should have been submitted.
+    expect(formSubmitted).toBe(true);
+  });
+});