diff --git a/packages/react-dom/src/__tests__/ReactDOM-test.js b/packages/react-dom/src/__tests__/ReactDOM-test.js
index fbb29f99d7c86..00356cc725392 100644
--- a/packages/react-dom/src/__tests__/ReactDOM-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOM-test.js
@@ -11,19 +11,25 @@
 
 let React;
 let ReactDOM;
+let ReactDOMClient;
 let ReactDOMServer;
 let ReactTestUtils;
 
+let act;
+
 describe('ReactDOM', () => {
   beforeEach(() => {
     jest.resetModules();
     React = require('react');
     ReactDOM = require('react-dom');
+    ReactDOMClient = require('react-dom/client');
     ReactDOMServer = require('react-dom/server');
     ReactTestUtils = require('react-dom/test-utils');
+
+    act = require('internal-test-utils').act;
   });
 
-  it('should bubble onSubmit', function () {
+  it('should bubble onSubmit', async () => {
     const container = document.createElement('div');
 
     let count = 0;
@@ -50,8 +56,11 @@ describe('ReactDOM', () => {
     }
 
     document.body.appendChild(container);
+    const root = ReactDOMClient.createRoot(container);
     try {
-      ReactDOM.render(<Parent />, container);
+      await act(() => {
+        root.render(<Parent />);
+      });
       buttonRef.click();
       expect(count).toBe(1);
     } finally {
@@ -228,7 +237,7 @@ describe('ReactDOM', () => {
     );
   });
 
-  it('preserves focus', () => {
+  it('preserves focus', async () => {
     let input;
     let input2;
     class A extends React.Component {
@@ -255,8 +264,11 @@ describe('ReactDOM', () => {
     const log = [];
     const container = document.createElement('div');
     document.body.appendChild(container);
+    const root = ReactDOMClient.createRoot(container);
     try {
-      ReactDOM.render(<A showTwo={false} />, container);
+      await act(() => {
+        root.render(<A showTwo={false} />);
+      });
       input.focus();
 
       // When the second input is added, let's simulate losing focus, which is
@@ -277,7 +289,9 @@ describe('ReactDOM', () => {
       });
 
       expect(document.activeElement.id).toBe('one');
-      ReactDOM.render(<A showTwo={true} />, container);
+      await act(() => {
+        root.render(<A showTwo={true} />);
+      });
       // input2 gets added, which causes input to get blurred. Then
       // componentDidUpdate focuses input2 and that should make it down to here,
       // not get overwritten by focus restoration.
@@ -288,7 +302,7 @@ describe('ReactDOM', () => {
     }
   });
 
-  it('calls focus() on autoFocus elements after they have been mounted to the DOM', () => {
+  it('calls focus() on autoFocus elements after they have been mounted to the DOM', async () => {
     const originalFocus = HTMLElement.prototype.focus;
 
     try {
@@ -305,14 +319,16 @@ describe('ReactDOM', () => {
 
       const container = document.createElement('div');
       document.body.appendChild(container);
-      ReactDOM.render(
-        <div>
-          <h1>Auto-focus Test</h1>
-          <input autoFocus={true} />
-          <p>The above input should be focused after mount.</p>
-        </div>,
-        container,
-      );
+      const root = ReactDOMClient.createRoot(container);
+      await act(() => {
+        root.render(
+          <div>
+            <h1>Auto-focus Test</h1>
+            <input autoFocus={true} />
+            <p>The above input should be focused after mount.</p>
+          </div>,
+        );
+      });
 
       expect(inputFocusedAfterMount).toBe(true);
       expect(focusedElement.tagName).toBe('INPUT');
@@ -321,7 +337,7 @@ describe('ReactDOM', () => {
     }
   });
 
-  it("shouldn't fire duplicate event handler while handling other nested dispatch", () => {
+  it("shouldn't fire duplicate event handler while handling other nested dispatch", async () => {
     const actual = [];
 
     class Wrapper extends React.Component {
@@ -352,8 +368,11 @@ describe('ReactDOM', () => {
 
     const container = document.createElement('div');
     document.body.appendChild(container);
+    const root = ReactDOMClient.createRoot(container);
     try {
-      ReactDOM.render(<Wrapper />, container);
+      await act(() => {
+        root.render(<Wrapper />);
+      });
 
       const expected = [
         '1st node clicked',
@@ -366,7 +385,7 @@ describe('ReactDOM', () => {
     }
   });
 
-  it('should not crash with devtools installed', () => {
+  it('should not crash with devtools installed', async () => {
     try {
       global.__REACT_DEVTOOLS_GLOBAL_HOOK__ = {
         inject: function () {},
@@ -382,14 +401,17 @@ describe('ReactDOM', () => {
           return <div />;
         }
       }
-      ReactDOM.render(<Component />, document.createElement('container'));
+      const root = ReactDOMClient.createRoot(document.createElement('div'));
+      await act(() => {
+        root.render(<Component />);
+      });
     } finally {
       delete global.__REACT_DEVTOOLS_GLOBAL_HOOK__;
     }
   });
 
-  it('should not crash calling findDOMNode inside a function component', () => {
-    const container = document.createElement('div');
+  it('should not crash calling findDOMNode inside a function component', async () => {
+    const root = ReactDOMClient.createRoot(document.createElement('div'));
 
     class Component extends React.Component {
       render() {
@@ -404,11 +426,13 @@ describe('ReactDOM', () => {
     };
 
     if (__DEV__) {
-      ReactDOM.render(<App />, container);
+      await act(() => {
+        root.render(<App />);
+      });
     }
   });
 
-  it('reports stacks with re-entrant renderToString() calls on the client', () => {
+  it('reports stacks with re-entrant renderToString() calls on the client', async () => {
     function Child2(props) {
       return <span ariaTypo3="no">{props.children}</span>;
     }
@@ -441,8 +465,12 @@ describe('ReactDOM', () => {
       );
     }
 
-    const container = document.createElement('div');
-    expect(() => ReactDOM.render(<App />, container)).toErrorDev([
+    const root = ReactDOMClient.createRoot(document.createElement('div'));
+    await expect(async () => {
+      await act(() => {
+        root.render(<App />);
+      });
+    }).toErrorDev([
       // ReactDOM(App > div > span)
       'Invalid ARIA attribute `ariaTypo`. ARIA attributes follow the pattern aria-* and must be lowercase.\n' +
         '    in span (at **)\n' +