It seems problematic to allow arbitary non-lowercase attribute on HTML nodes. Because the server has no ability to keep them case sensitive (HTML isn't). So they will end up different on the client.

We should probably warn if the attribute is not a known one *and* is not lowercase.
const e = await render(
          <input type="checkbox" checked={true} readOnly={true} />,
        );
        expect(e.checked).toBe(true);
      });
      itRenders(
        'a checkbox that is checked and no onChange/readOnly',
        async render => {
          
          
          const e = await render(<input type="checkbox" checked={true} />, 1);
          expect(e.checked).toBe(true);
        },
      );
      itRenders('a checkbox with defaultChecked', async render => {
        const e = await render(<input type="checkbox" defaultChecked={true} />);
        expect(e.checked).toBe(true);
        expect(e.getAttribute('defaultChecked')).toBe(null);
      });
      itRenders(
        'a checkbox checked overriding defaultChecked',
        async render => {
          const e = await render(
            <input
              type="checkbox"
              checked={true}
              defaultChecked={false}
              readOnly={true}
            />,
            1,