have you considered when the post comment number is 1, so it is comment without 's'

[zzz6519003]

    it('should correctly render the footer text comments as plural for multiple comments', function () {
         var post = {
             points:         5,
             postedBy:       'Prabir Shrestha',
             postedAgo:      '4 hours ago',
             commentCount:   7
         };

        var footer = TestUtils.renderIntoDocument(<Footer post={post} />);
        var small = TestUtils.findRenderedDOMComponentWithTag(footer, 'small');
        var text = small.getDOMNode().textContent;

        expect(text.indexOf('comments', text.length - 'comments'.length)).not.toBe(-1);

notice the line expect(text.indexOf('comments', text.length - 'comments'.length)).not.toBe(-1);

have you considered when the post comment number is 1, so it is comment without 's'