expose TestUtils.act() for batching actions in tests

packages/react-debug-tools/src/__tests__/ReactHooksInspectionIntegration-test.js

@@ -13,12 +13,14 @@
 let React;
 let ReactTestRenderer;
 let ReactDebugTools;
+let act;
 
-describe('ReactHooksInspectionIntergration', () => {
+describe('ReactHooksInspectionIntegration', () => {
   beforeEach(() => {
     jest.resetModules();
     React = require('react');
     ReactTestRenderer = require('react-test-renderer');
+    act = ReactTestRenderer.act;
     ReactDebugTools = require('react-debug-tools');
   });
 
@@ -47,7 +49,7 @@ describe('ReactHooksInspectionIntergration', () => {
       onMouseUp: setStateB,
     } = renderer.root.findByType('div').props;
 
-    setStateA('Hi');
+    act(() => setStateA('Hi'));
 
     childFiber = renderer.root.findByType(Foo)._currentFiber();
     tree = ReactDebugTools.inspectHooksOfFiber(childFiber);
@@ -57,7 +59,7 @@ describe('ReactHooksInspectionIntergration', () => {
       {name: 'State', value: 'world', subHooks: []},
     ]);
 
-    setStateB('world!');
+    act(() => setStateB('world!'));
 
     childFiber = renderer.root.findByType(Foo)._currentFiber();
     tree = ReactDebugTools.inspectHooksOfFiber(childFiber);
@@ -91,8 +93,12 @@ describe('ReactHooksInspectionIntergration', () => {
       React.useMemo(() => state1 + state2, [state1]);
 
       function update() {
-        setState('A');
-        dispatch({value: 'B'});
+        act(() => {
+          setState('A');
+        });
+        act(() => {
+          dispatch({value: 'B'});
+        });
         ref.current = 'C';
       }
       let memoizedUpdate = React.useCallback(update, []);

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

@@ -13,7 +13,9 @@ let React;
 let ReactDOM;
 let Suspense;
 let ReactCache;
+let ReactTestUtils;
 let TextResource;
+let act;
 
 describe('ReactDOMSuspensePlaceholder', () => {
   let container;
@@ -23,6 +25,8 @@ describe('ReactDOMSuspensePlaceholder', () => {
     React = require('react');
     ReactDOM = require('react-dom');
     ReactCache = require('react-cache');
+    ReactTestUtils = require('react-dom/test-utils');
+    act = ReactTestUtils.act;
     Suspense = React.Suspense;
     container = document.createElement('div');
     document.body.appendChild(container);
@@ -142,12 +146,14 @@ describe('ReactDOMSuspensePlaceholder', () => {
         );
       }
 
-      ReactDOM.render(<App />, container);
+      act(() => {
+        ReactDOM.render(<App />, container);
+      });
       expect(container.innerHTML).toEqual(
         '<span style="display: none;">Sibling</span><span style="display: none;"></span>Loading...',
       );
 
-      setIsVisible(true);
+      act(() => setIsVisible(true));
       expect(container.innerHTML).toEqual(
         '<span style="display: none;">Sibling</span><span style="display: none;"></span>Loading...',
       );

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

@@ -14,6 +14,7 @@ let React;
 let ReactDOM;
 let ReactDOMServer;
 let ReactTestUtils;
+let act;
 
 function getTestDocument(markup) {
   const doc = document.implementation.createHTMLDocument('');
@@ -33,6 +34,7 @@ describe('ReactTestUtils', () => {
     ReactDOM = require('react-dom');
     ReactDOMServer = require('react-dom/server');
     ReactTestUtils = require('react-dom/test-utils');
+    act = ReactTestUtils.act;
   });
 
   it('Simulate should have locally attached media events', () => {
@@ -515,4 +517,168 @@ describe('ReactTestUtils', () => {
     ReactTestUtils.renderIntoDocument(<Component />);
     expect(mockArgs.length).toEqual(0);
   });
+
+  it('can use act to batch effects', () => {
+    function App(props) {
+      React.useEffect(props.callback);
+      return null;
+    }
+    const container = document.createElement('div');
+    document.body.appendChild(container);
+
+    try {
+      let called = false;
+      act(() => {
+        ReactDOM.render(
+          <App
+            callback={() => {
+              called = true;
+            }}
+          />,
+          container,
+        );
+      });
+
+      expect(called).toBe(true);
+    } finally {
+      document.body.removeChild(container);
+    }
+  });
+
+  it('flushes effects on every call', () => {
+    function App(props) {
+      let [ctr, setCtr] = React.useState(0);
+      React.useEffect(() => {
+        props.callback(ctr);
+      });
+      return (
+        <button id="button" onClick={() => setCtr(x => x + 1)}>
+          click me!
+        </button>
+      );
+    }
+
+    const container = document.createElement('div');
+    document.body.appendChild(container);
+    let calledCtr = 0;
+    act(() => {
+      ReactDOM.render(
+        <App
+          callback={val => {
+            calledCtr = val;
+          }}
+        />,
+        container,
+      );
+    });
+    const button = document.getElementById('button');
+    function click() {
+      button.dispatchEvent(new MouseEvent('click', {bubbles: true}));
+    }
+
+    act(() => {
+      click();
+      click();
+      click();
+    });
+    expect(calledCtr).toBe(3);
+    act(click);
+    expect(calledCtr).toBe(4);
+    act(click);
+    expect(calledCtr).toBe(5);
+
+    document.body.removeChild(container);
+  });
+
+  it('can use act to batch effects on updates too', () => {
+    function App() {
+      let [ctr, setCtr] = React.useState(0);
+      return (
+        <button id="button" onClick={() => setCtr(x => x + 1)}>
+          {ctr}
+        </button>
+      );
+    }
+    const container = document.createElement('div');
+    document.body.appendChild(container);
+    let button;
+    act(() => {
+      ReactDOM.render(<App />, container);
+    });
+    button = document.getElementById('button');
+    expect(button.innerHTML).toBe('0');
+    act(() => {
+      button.dispatchEvent(new MouseEvent('click', {bubbles: true}));
+    });
+    expect(button.innerHTML).toBe('1');
+    document.body.removeChild(container);
+  });
+
+  it('detects setState being called outside of act(...)', () => {
+    let setValueRef = null;
+    function App() {
+      let [value, setValue] = React.useState(0);
+      setValueRef = setValue;
+      return (
+        <button id="button" onClick={() => setValue(2)}>
+          {value}
+        </button>
+      );
+    }
+    const container = document.createElement('div');
+    document.body.appendChild(container);
+    let button;
+    act(() => {
+      ReactDOM.render(<App />, container);
+      button = container.querySelector('#button');
+      button.dispatchEvent(new MouseEvent('click', {bubbles: true}));
+    });
+    expect(button.innerHTML).toBe('2');
+    expect(() => setValueRef(1)).toWarnDev(
+      ['An update to App inside a test was not wrapped in act(...).'],
+      {withoutStack: 1},
+    );
+    document.body.removeChild(container);
+  });
+
+  it('lets a ticker update', () => {
+    function App() {
+      let [toggle, setToggle] = React.useState(0);
+      React.useEffect(() => {
+        let timeout = setTimeout(() => {
+          setToggle(1);
+        }, 200);
+        return () => clearTimeout(timeout);
+      });
+      return toggle;
+    }
+    const container = document.createElement('div');
+
+    act(() => {
+      act(() => {
+        ReactDOM.render(<App />, container);
+      });
+      jest.advanceTimersByTime(250);
+    });
+
+    expect(container.innerHTML).toBe('1');
+  });
+
+  it('warns if you return a value inside act', () => {
+    expect(() => act(() => 123)).toWarnDev(
+      [
+        'The callback passed to ReactTestUtils.act(...) function must not return anything.',
+      ],
+      {withoutStack: true},
+    );
+  });
+
+  it('warns if you try to await an .act call', () => {
+    expect(act(() => {}).then).toWarnDev(
+      [
+        'Do not await the result of calling ReactTestUtils.act(...), it is not a Promise.',
+      ],
+      {withoutStack: true},
+    );
+  });
 });

packages/react-dom/src/test-utils/ReactTestUtils.js

@@ -18,9 +18,15 @@ import {
 import SyntheticEvent from 'events/SyntheticEvent';
 import invariant from 'shared/invariant';
 import lowPriorityWarning from 'shared/lowPriorityWarning';
+import warningWithoutStack from 'shared/warningWithoutStack';
 import {ELEMENT_NODE} from '../shared/HTMLNodeType';
 import * as DOMTopLevelEventTypes from '../events/DOMTopLevelEventTypes';
 
+// for .act's return value
+type Thenable = {
+  then(resolve: () => mixed, reject?: () => mixed): mixed,
+};
+
 const {findDOMNode} = ReactDOM;
 // Keep in sync with ReactDOMUnstableNativeDependencies.js
 // and ReactDOM.js:
@@ -145,6 +151,9 @@ function validateClassInstance(inst, methodName) {
   );
 }
 
+// stub element used by act() when flushing effects
+let actContainerElement = document.createElement('div');
+
 /**
  * Utilities for making it easy to test React components.
  *
@@ -380,6 +389,43 @@ const ReactTestUtils = {
 
   Simulate: null,
   SimulateNative: {},
+
+  act(callback: () => void): Thenable {
+    // note: keep these warning messages in sync with
+    // createReactNoop.js and ReactTestRenderer.js
+    const result = ReactDOM.unstable_batchedUpdates(callback);
+    if (__DEV__) {
+      if (result !== undefined) {
+        let addendum;
+        if (typeof result.then === 'function') {
+          addendum =
+            '\n\nIt looks like you wrote ReactTestUtils.act(async () => ...), ' +
+            'or returned a Promise from the callback passed to it. ' +
+            'Putting asynchronous logic inside ReactTestUtils.act(...) is not supported.\n';
+        } else {
+          addendum = ' You returned: ' + result;
+        }
+        warningWithoutStack(
+          false,
+          'The callback passed to ReactTestUtils.act(...) function must not return anything.%s',
+          addendum,
+        );
+      }
+    }
+    ReactDOM.render(<div />, actContainerElement);
+    // we want the user to not expect a return,
+    // but we want to warn if they use it like they can await on it.
+    return {
+      then() {
+        if (__DEV__) {
+          warningWithoutStack(
+            false,
+            'Do not await the result of calling ReactTestUtils.act(...), it is not a Promise.',
+          );
+        }
+      },
+    };
+  },
 };
 
 /**

packages/react-noop-renderer/src/createReactNoop.js

@@ -21,6 +21,12 @@ import type {ReactNodeList} from 'shared/ReactTypes';
 import {createPortal} from 'shared/ReactPortal';
 import expect from 'expect';
 import {REACT_FRAGMENT_TYPE, REACT_ELEMENT_TYPE} from 'shared/ReactSymbols';
+import warningWithoutStack from 'shared/warningWithoutStack';
+
+// for .act's return value
+type Thenable = {
+  then(resolve: () => mixed, reject?: () => mixed): mixed,
+};
 
 type Container = {
   rootID: string,
@@ -864,6 +870,43 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
 
     interactiveUpdates: NoopRenderer.interactiveUpdates,
 
+    // maybe this should exist only in the test file
+    act(callback: () => void): Thenable {
+      // note: keep these warning messages in sync with
+      // ReactTestRenderer.js and ReactTestUtils.js
+      let result = NoopRenderer.batchedUpdates(callback);
+      if (__DEV__) {
+        if (result !== undefined) {
+          let addendum;
+          if (typeof result.then === 'function') {
+            addendum =
+              "\n\nIt looks like you wrote ReactNoop.act(async () => ...) or returned a Promise from it's callback. " +
+              'Putting asynchronous logic inside ReactNoop.act(...) is not supported.\n';
+          } else {
+            addendum = ' You returned: ' + result;
+          }
+          warningWithoutStack(
+            false,
+            'The callback passed to ReactNoop.act(...) function must not return anything.%s',
+            addendum,
+          );
+        }
+      }
+      ReactNoop.flushPassiveEffects();
+      // we want the user to not expect a return,
+      // but we want to warn if they use it like they can await on it.
+      return {
+        then() {
+          if (__DEV__) {
+            warningWithoutStack(
+              false,
+              'Do not await the result of calling ReactNoop.act(...), it is not a Promise.',
+            );
+          }
+        },
+      };
+    },
+
     flushSync(fn: () => mixed) {
       yieldedValues = [];
       NoopRenderer.flushSync(fn);