1. In a bowl, combine black beans, cannellini beans, garbanzo beans, green beans, and onion; stir to evenly combine.
2. In a medium saucepan over medium-high heat, combine vinegar and sugar; stir frequently for about 4 to 5 minutes, making sure the sugar dissolves in the vinegar.
3. Pour the vinegar-sugar mixture over the beans and onions. Add in salt and pepper; stir until well combined.
4. Chill for 2 hours then enjoy!
Source of recipe: This recipe is from my stepfather-in-law. I was glad that he made this when we came up for the holidays. I lived on this for lunch for days. This recipe is very easy to make and will last a long time in the refrigerator. It is also very easy to change up this recipe and add different beans or vinegar to create a different taste. I hope you enjoy!