See the original report in https://github.com/facebook/react/issues/10772#issuecomment-333242375.

The problem is that SVG is case sensitive, and so naïvely setting `tabIndex` and relying on insensitivity won't work with it.

The good news is it seems like `tabindex` is the only valid [SVG attribute](https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute) with this problem. We just missed it because it applies both to HTML and SVG.

I think the fix is to add it back to the whitelist. 
if (
          render === serverRender ||
          render === clientRenderOnServerString ||
          render === streamRender
        ) {
          expect(e.childNodes.length).toBe(3);
          expectTextNode(e.childNodes[0], '<span>Text1&quot;</span>');
          expectTextNode(e.childNodes[2], '<span>Text2&quot;</span>');
        } else {
          expect(e.childNodes.length).toBe(2);
          expectTextNode(e.childNodes[0], '<span>Text1&quot;</span>');
          expectTextNode(e.childNodes[1], '<span>Text2&quot;</span>');
        }
      });
    });
    describe('components that throw errors', function() {
      itThrowsWhenRendering(
        'a function returning undefined',
        async render => {
          const UndefinedComponent = () => undefined;
          await render(<UndefinedComponent />, 1);
        },
        'UndefinedComponent(...): Nothing was returned from render. ' +
          'This usually means a return statement is missing. Or, to ' +
          'render nothing, return null.',
      );
      itThrowsWhenRendering(
        'a class returning undefined',
        async render => {
          class UndefinedComponent extends React.Component {