title: Faced error during testing with Jest and Enzyme in React
body: <p>I was learning how to test React app, that is, to test if props is assigned to component. Here is the code:</p>
  
  <pre><code>import React from "react";
  
  import { configure, shallow } from "enzyme";
  import Adapter from "enzyme-adapter-react-16";
  import Footer from "../Footer/Footer";
  configure({ adapter: new Adapter() });
  
  describe("&lt;About /&gt;", () =&gt; {
    it("check the type of value", () =&gt; {
      const props = {
        copyright: "All rights reserved"
      };
      const footer = shallow(&lt;Footer {...props} /&gt;);
      expect(footer.prop("copyright")).toBeString(); //Here the error is shown saying something is wrong with tobeString().
    });
  });
  </code></pre>
  
  <p><strong>Footer component</strong></p>
  
  <p>**</p>
  
  <pre><code>import React from "react";
  import styles from "./Footer.module.css";
  import { PropTypes } from "prop-types";
  const Footer = ({ copyright }) =&gt; {
    return (
      &lt;footer className={styles.footer}&gt;
        &lt;p&gt;{copyright}&lt;/p&gt;
      &lt;/footer&gt;
    );
  };
  Footer.propTypes = {
    copyright: PropTypes.string.isRequired
  };
  export default Footer;
  </code></pre>
  
  <p>**</p>
  
  <p>As you can see the code above in the first code block, tobeString() is said to be an ERROR</p>