Even narrower viewports exist. KaiOS devices tend to have 240 px viewports; smartwatches tend to have half the width of a phone while emulating a phone width (Apple Watches can be instructed not to do this with a proprietary `meta` tag). Of course, making sites watch-compatible is a stretch, but support for feature phones running KaiOS should be reasonable. I wrote about this more in <cite>[Best practices for inclusive textual websites]({{<relref"/posts/website-best-practices">}})</cite>.
Another thing worth remembering is that users can change default fonts or override sire-set fonts. Don't just test with default default fonts; test with something wider. These criteria should specify some font metrics or (royalty free) representative wide fonts to use for testing.
