make testing builds for React/ReactDOM

This PR introduces adds `react/testing` and `react-dom/testing`.
- changes infra to generate these builds
- exports act on ReactDOM in these testing builds
- uses the new test builds in fixtures/dom

In the next PR -

- I'll use the new builds for all our own tests
- I'll replace usages of TestUtils.act with ReactDOM.act.

fixtures/dom/src/__tests__/nested-act-test.js

@@ -8,18 +8,23 @@
  */
 
 let React;
-let TestUtils;
+let ReactDOM;
 let TestRenderer;
 
 global.__DEV__ = process.env.NODE_ENV !== 'production';
 
+jest.mock('react-dom', () =>
+  require.requireActual('react-dom/cjs/react-dom-testing.development.js')
+);
+// we'll replace the above with react/testing and react-dom/testing right before the next minor
+
 expect.extend(require('../toWarnDev'));
 
 describe('unmocked scheduler', () => {
   beforeEach(() => {
     jest.resetModules();
     React = require('react');
-    TestUtils = require('react-dom/test-utils');
+    ReactDOM = require('react-dom');
     TestRenderer = require('react-test-renderer');
   });
 
@@ -33,7 +38,7 @@ describe('unmocked scheduler', () => {
     }
     // in legacy mode, this tests whether an act only flushes its own effects
     TestRenderer.act(() => {
-      TestUtils.act(() => {
+      ReactDOM.act(() => {
         TestRenderer.create(<Effecty />);
       });
       expect(log).toEqual([]);
@@ -42,7 +47,7 @@ describe('unmocked scheduler', () => {
 
     log = [];
     // for doublechecking, we flip it inside out, and assert on the outermost
-    TestUtils.act(() => {
+    ReactDOM.act(() => {
       TestRenderer.act(() => {
         TestRenderer.create(<Effecty />);
       });
@@ -59,7 +64,7 @@ describe('mocked scheduler', () => {
       require.requireActual('scheduler/unstable_mock')
     );
     React = require('react');
-    TestUtils = require('react-dom/test-utils');
+    ReactDOM = require('react-dom');
     TestRenderer = require('react-test-renderer');
   });
 
@@ -77,7 +82,7 @@ describe('mocked scheduler', () => {
     }
     // with a mocked scheduler, this tests whether it flushes all work only on the outermost act
     TestRenderer.act(() => {
-      TestUtils.act(() => {
+      ReactDOM.act(() => {
         TestRenderer.create(<Effecty />);
       });
       expect(log).toEqual([]);
@@ -86,7 +91,7 @@ describe('mocked scheduler', () => {
 
     log = [];
     // for doublechecking, we flip it inside out, and assert on the outermost
-    TestUtils.act(() => {
+    ReactDOM.act(() => {
       TestRenderer.act(() => {
         TestRenderer.create(<Effecty />);
       });

fixtures/dom/src/__tests__/wrong-act-test.js

@@ -12,13 +12,17 @@ let ReactDOM;
 let ReactART;
 let ARTSVGMode;
 let ARTCurrentMode;
-let TestUtils;
 let TestRenderer;
 let ARTTest;
 
 global.__DEV__ = process.env.NODE_ENV !== 'production';
 global.__EXPERIMENTAL__ = process.env.RELEASE_CHANNEL === 'experimental';
 
+jest.mock('react-dom', () =>
+  require.requireActual('react-dom/cjs/react-dom-testing.development.js')
+);
+// we'll replace the above with react/testing and react-dom/testing right before the next minor
+
 expect.extend(require('../toWarnDev'));
 
 function App(props) {
@@ -32,7 +36,6 @@ beforeEach(() => {
   ReactART = require('react-art');
   ARTSVGMode = require('art/modes/svg');
   ARTCurrentMode = require('art/modes/current');
-  TestUtils = require('react-dom/test-utils');
   TestRenderer = require('react-test-renderer');
 
   ARTCurrentMode.setCurrent(ARTSVGMode);
@@ -70,8 +73,8 @@ beforeEach(() => {
 });
 
 it("doesn't warn when you use the right act + renderer: dom", () => {
-  TestUtils.act(() => {
-    TestUtils.renderIntoDocument(<App />);
+  ReactDOM.act(() => {
+    ReactDOM.render(<App />, document.createElement('div'));
   });
 });
 
@@ -86,7 +89,7 @@ it('resets correctly across renderers', () => {
     React.useEffect(() => {}, []);
     return null;
   }
-  TestUtils.act(() => {
+  ReactDOM.act(() => {
     TestRenderer.act(() => {});
     expect(() => {
       TestRenderer.create(<Effecty />);
@@ -99,7 +102,7 @@ it('resets correctly across renderers', () => {
 it('warns when using the wrong act version - test + dom: render', () => {
   expect(() => {
     TestRenderer.act(() => {
-      TestUtils.renderIntoDocument(<App />);
+      ReactDOM.render(<App />, document.createElement('div'));
     });
   }).toWarnDev(["It looks like you're using the wrong act()"], {
     withoutStack: true,
@@ -113,7 +116,7 @@ it('warns when using the wrong act version - test + dom: updates', () => {
     setCtr = _setCtr;
     return ctr;
   }
-  TestUtils.renderIntoDocument(<Counter />);
+  ReactDOM.render(<Counter />, document.createElement('div'));
   expect(() => {
     TestRenderer.act(() => {
       setCtr(1);
@@ -123,7 +126,7 @@ it('warns when using the wrong act version - test + dom: updates', () => {
 
 it('warns when using the wrong act version - dom + test: .create()', () => {
   expect(() => {
-    TestUtils.act(() => {
+    ReactDOM.act(() => {
       TestRenderer.create(<App />);
     });
   }).toWarnDev(["It looks like you're using the wrong act()"], {
@@ -134,7 +137,7 @@ it('warns when using the wrong act version - dom + test: .create()', () => {
 it('warns when using the wrong act version - dom + test: .update()', () => {
   const root = TestRenderer.create(<App key="one" />);
   expect(() => {
-    TestUtils.act(() => {
+    ReactDOM.act(() => {
       root.update(<App key="two" />);
     });
   }).toWarnDev(["It looks like you're using the wrong act()"], {
@@ -151,15 +154,15 @@ it('warns when using the wrong act version - dom + test: updates', () => {
   }
   TestRenderer.create(<Counter />);
   expect(() => {
-    TestUtils.act(() => {
+    ReactDOM.act(() => {
       setCtr(1);
     });
   }).toWarnDev(["It looks like you're using the wrong act()"]);
 });
 
 it('does not warn when nesting react-act inside react-dom', () => {
-  TestUtils.act(() => {
-    TestUtils.renderIntoDocument(<ARTTest />);
+  ReactDOM.act(() => {
+    ReactDOM.render(<ARTTest />, document.createElement('div'));
   });
 });
 
@@ -171,7 +174,7 @@ it('does not warn when nesting react-act inside react-test-renderer', () => {
 
 it("doesn't warn if you use nested acts from different renderers", () => {
   TestRenderer.act(() => {
-    TestUtils.act(() => {
+    ReactDOM.act(() => {
       TestRenderer.create(<App />);
     });
   });

packages/react-dom/npm/testing.js

@@ -0,0 +1,38 @@
+'use strict';
+
+function checkDCE() {
+  /* global __REACT_DEVTOOLS_GLOBAL_HOOK__ */
+  if (
+    typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ === 'undefined' ||
+    typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.checkDCE !== 'function'
+  ) {
+    return;
+  }
+  if (process.env.NODE_ENV !== 'production') {
+    // This branch is unreachable because this function is only called
+    // in production, but the condition is true only in development.
+    // Therefore if the branch is still here, dead code elimination wasn't
+    // properly applied.
+    // Don't change the message. React DevTools relies on it. Also make sure
+    // this message doesn't occur elsewhere in this function, or it will cause
+    // a false positive.
+    throw new Error('^_^');
+  }
+  try {
+    // Verify that the code above has been dead code eliminated (DCE'd).
+    __REACT_DEVTOOLS_GLOBAL_HOOK__.checkDCE(checkDCE);
+  } catch (err) {
+    // DevTools shouldn't crash React, no matter what.
+    // We should still report in case we break this code.
+    console.error(err);
+  }
+}
+
+if (process.env.NODE_ENV === 'production') {
+  // DCE check should happen before ReactDOM bundle executes so that
+  // DevTools can report bad minification during injection.
+  checkDCE();
+  module.exports = require('./cjs/react-dom-testing.production.min.js');
+} else {
+  module.exports = require('./cjs/react-dom-testing.development.js');
+}

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

@@ -722,6 +722,7 @@ function runActTests(label, render, unmount, rerender) {
 
     describe('suspense', () => {
       if (__DEV__ && __EXPERIMENTAL__) {
+        // todo - remove __DEV__ check once we start using testing builds
         it('triggers fallbacks if available', async () => {
           let resolved = false;
           let resolve;

packages/react-dom/src/client/ReactDOM.js

@@ -35,6 +35,7 @@ import {
   attemptUserBlockingHydration,
   attemptContinuousHydration,
   attemptHydrationAtCurrentPriority,
+  act,
 } from 'react-reconciler/inline.dom';
 import {createPortal as createPortalImpl} from 'shared/ReactPortal';
 import {canUseDOM} from 'shared/ExecutionEnvironment';
@@ -58,6 +59,7 @@ import {
   disableUnstableCreatePortal,
   disableUnstableRenderSubtreeIntoContainer,
   warnUnstableRenderSubtreeIntoContainer,
+  isTestEnvironment,
 } from 'shared/ReactFeatureFlags';
 
 import {
@@ -249,4 +251,8 @@ if (__DEV__) {
   }
 }
 
+if (isTestEnvironment) {
+  ReactDOM.act = act;
+}
+
 export default ReactDOM;

packages/react-dom/testing.js

@@ -0,0 +1,16 @@
+/**
+ * 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.
+ *
+ * @flow
+ */
+
+'use strict';
+
+const ReactDOM = require('./src/client/ReactDOM');
+
+// TODO: decide on the top-level export form.
+// This is hacky but makes it work with both Rollup and Jest.
+module.exports = ReactDOM.default || ReactDOM;