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.
expect(e.getAttribute('value')).toBe(null);
        expect(e.getAttribute('defaultValue')).toBe(null);
        expect(e.value).toBe('foo');
      });
      itRenders(
        'a textarea value overriding defaultValue no matter the prop order',
        async render => {
          const e = await render(
            <textarea defaultValue="bar" value="foo" readOnly={true} />,
            1,
          );
          expect(e.getAttribute('value')).toBe(null);
          expect(e.getAttribute('defaultValue')).toBe(null);
          expect(e.value).toBe('foo');
        },
      );
    });
    describe('selects', function() {
      var options;
      beforeEach(function() {
        options = [
          <option key={1} value="foo" id="foo">Foo</option>,
          <option key={2} value="bar" id="bar">Bar</option>,
          <option key={3} value="baz" id="baz">Baz</option>,
        ];
      });
      
      
      
      const expectSelectValue = (element, selected) => {