Tooltip tests not passing

JavaScript
1

Tell us what’s happening:
The tests for D3: Heat Map are not passing, even though the tooltip is working.
What am I doing wrong?

Your code so far
This is the part which is doing the tooltip, I’m appending to rect elements.

       .append("title")
        .attr("id","tooltip")
        .attr("data-year", (d) => { return d.year  })
        .text((d) => {
        return (d.year) + "\n" + (baseTemperature + d.variance).toFixed(2) + " °C";
      });

This is the code on codepen: https://codepen.io/imestin/pen/qBOpodX
Your browser information:

User Agent is: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Firefox/68.0.

Challenge: Visualize Data with a Heat Map

Link to the challenge: