Line test
This line chart shows one week of temperature in degrees Celsius for San Francisco, with a smooth curve and an interactive tooltip that displays the date and value as the mouse moves. The visualization is rendered as an SVG and built with D3 v3, using `scaleTime`, `scaleLinear`, `axisBottom`, `axisLeft`, and a `line` generator with `curveBasis`. Data is loaded from a CSV file via `d3.csv`, and the tooltip is implemented with `d3.mouse` and SVG text/path elements.