Use testing builds for our own tests

Following up from facebook#17915 where we generated testing builds for `react-dom`, this PR uses those builds for our own tests.

- fixes `ReactFeatureFlags.testing` to use all the default flags
- changes `ReactFeatureFlags.readonly` to return `isTestEnvironment: true` (this might not strictly be needed)
- with jest, mocks `react-dom` with the testing version, both for source and builds
- uses `ReactDOM.act` in one of these tests to verify it actually works

Author: threepointone

.eslintrc.js

@@ -168,6 +168,7 @@ module.exports = {
     __PROFILE__: true,
     __UMD__: true,
     __EXPERIMENTAL__: true,
+    __TEST__: true,
     trustedTypes: true,
   },
 };

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

@@ -13,10 +13,7 @@ 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
+jest.mock('react-dom', () => require.requireActual('react-dom/testing.js'));
 
 expect.extend(require('../toWarnDev'));
 

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

@@ -18,10 +18,7 @@ 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
+jest.mock('react-dom', () => require.requireActual('react-dom/testing.js'));
 
 expect.extend(require('../toWarnDev'));
 

packages/react-dom/package.json

@@ -30,6 +30,7 @@
     "README.md",
     "build-info.json",
     "index.js",
+    "testing.js",
     "profiling.js",
     "server.js",
     "server.browser.js",

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

@@ -13,7 +13,6 @@ let React;
 let ReactDOM;
 let Suspense;
 let ReactCache;
-let ReactTestUtils;
 let Scheduler;
 let TextResource;
 let act;
@@ -26,9 +25,8 @@ describe('ReactDOMSuspensePlaceholder', () => {
     React = require('react');
     ReactDOM = require('react-dom');
     ReactCache = require('react-cache');
-    ReactTestUtils = require('react-dom/test-utils');
     Scheduler = require('scheduler');
-    act = ReactTestUtils.act;
+    act = ReactDOM.act;
     Suspense = React.Suspense;
     container = document.createElement('div');
     document.body.appendChild(container);

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

@@ -59,7 +59,6 @@ import {
   disableUnstableCreatePortal,
   disableUnstableRenderSubtreeIntoContainer,
   warnUnstableRenderSubtreeIntoContainer,
-  isTestEnvironment,
 } from 'shared/ReactFeatureFlags';
 
 import {
@@ -253,7 +252,7 @@ if (__DEV__) {
   }
 }
 
-if (isTestEnvironment) {
+if (__TEST__) {
   ReactDOM.act = act;
 }
 

packages/react-reconciler/src/ReactFiberReconciler.js

@@ -87,10 +87,10 @@ import {
   findHostInstancesForRefresh,
 } from './ReactFiberHotReloading';
 
-// used by isTestEnvironment builds
+// used by __TEST__ builds
 import enqueueTask from 'shared/enqueueTask';
 import * as Scheduler from 'scheduler';
-// end isTestEnvironment imports
+// end __TEST__ imports
 
 type OpaqueRoot = FiberRoot;
 

packages/shared/forks/ReactFeatureFlags.native-fb.js

@@ -52,7 +52,6 @@ export const disableUnstableRenderSubtreeIntoContainer = false;
 export const warnUnstableRenderSubtreeIntoContainer = false;
 export const disableUnstableCreatePortal = false;
 export const deferPassiveEffectCleanupDuringUnmount = false;
-export const isTestEnvironment = false;
 
 // Only used in www builds.
 export function addUserTimingListener() {

packages/shared/forks/ReactFeatureFlags.native-oss.js

@@ -47,7 +47,6 @@ export const disableUnstableRenderSubtreeIntoContainer = false;
 export const warnUnstableRenderSubtreeIntoContainer = false;
 export const disableUnstableCreatePortal = false;
 export const deferPassiveEffectCleanupDuringUnmount = false;
-export const isTestEnvironment = false;
 
 // Only used in www builds.
 export function addUserTimingListener() {

packages/shared/forks/ReactFeatureFlags.persistent.js

@@ -47,7 +47,6 @@ export const disableUnstableRenderSubtreeIntoContainer = false;
 export const warnUnstableRenderSubtreeIntoContainer = false;
 export const disableUnstableCreatePortal = false;
 export const deferPassiveEffectCleanupDuringUnmount = false;
-export const isTestEnvironment = false;
 
 // Only used in www builds.
 export function addUserTimingListener() {