What would the pattern be for this??

I want to knit an official swatch instead of just doing stockinette again and again.. I want to knit something that has nice edges like this to prevent my edges from rolling. The idea is essentially a mini blanket! What pattern would the border be?? Or is there a place that has patterns for something like this?

I want to knit an official swatch instead of just doing stockinette again and again.. I want to knit something that has nice edges like this to prevent my edges from rolling. The idea is essentially a mini blanket! What pattern would the border be?? Or is there a place that has patterns for something like this?