title: @testing-library/jest-dom not loading
body: <p>I'm trying to introduce React Testing Library into Create React App project, and I'm hitting a strange problem. For one of my tests, I need to use jest-dom, but I can't seem to import it successfully.</p>
  
  <p>I've <code>yarn add</code>'ed it, and can't think of what step I missed.
  <code>expect.extend</code> fails because its <code>toHaveStyle</code> is undefined.</p>
  
  <p>Here's my test file, reduced down to the minimum:</p>
  
  <pre><code>import React from 'react';
  import {render, screen} from '@testing-library/react';
  
  import {toHaveStyle} from '@testing-library/jest-dom';
  import '@testing-library/jest-dom/extend-expect';
  //expect.extend({toHaveStyle});
  
  it('is confusing me', () =&gt; {
    // (Using `toBe(42) as an ersatz `console.log`)
    expect([Object.keys(require('@testing-library/jest-dom')), Object.keys(require('@testing-library/react')), toHaveClass]).toBe(42);
  });
  </code></pre>
  
  <p>The output is:</p>
  
  <pre><code>  Expected: 42
      Received: [[], ["render", "cleanup", "fireEvent", ...], undefined]
  </code></pre>
  
  <p>And, here's the relevant part of yarn.lock:</p>
  
  <pre><code>"@testing-library/jest-dom@^5.7.0":
    version "5.7.0"
    resolved "https://registry.yarnpkg.com/@testing-library/jest-dom/-/jest-dom-5.7.0.tgz#b2e2acb4c088a293d52ba2cd1674b526282a2f87"
    integrity sha512-ZV0OtBXmTDEDxrIbqJXiOcXCZ6aIMpmDlmfHj0hGNsSuQ/nX0qPAs9HWmCzXvPfTrhufTiH2nJLvDJu/LgHzwQ==
    dependencies:
      "@babel/runtime" "^7.9.2"
      "@types/testing-library__jest-dom" "^5.0.2"
      chalk "^3.0.0"
      css "^2.2.4"
      css.escape "^1.5.1"
      jest-diff "^25.1.0"
      jest-matcher-utils "^25.1.0"
      lodash "^4.17.15"
      redent "^3.0.0"
  
  "@testing-library/react@^10.0.4":
    version "10.0.4"
    resolved "https://registry.yarnpkg.com/@testing-library/react/-/react-10.0.4.tgz#8e0e299cd91acc626d81ed8489fdc13df864c31d"
    integrity sha512-2e1B5debfuiIGbvUuiSXybskuh7ZTVJDDvG/IxlzLOY9Co/mKFj9hIklAe2nGZYcOUxFaiqWrRZ9vCVGzJfRlQ==
    dependencies:
      "@babel/runtime" "^7.9.6"
      "@testing-library/dom" "^7.2.2"
      "@types/testing-library__react" "^10.0.1"
  </code></pre>