Some users might want to download the charts on the statistics page (https://hashtags.wmflabs.org/graph/?query=test) as images, so we should allow this. Each graph shown to users should, under the Download CSV button, have a Download Image button which downloads that chart as a jpg file with an appropriate file name.
Additionally, a test should be written which confirms this behaviour downloads a file as expected. Testing the contents of that file may be hard, so confirming the download of a file is sufficient.
The guide at https://www.codeproject.com/Tips/1120045/Export-Chart-js-Charts-as-Image may be helpful.