Quarter the cherry tomatoes. Mix the olive oil, vinegar, sugar, parsley, garlic and mustard well in a bowl. Add the cocktail tomatoes to the sauce and stir again. Then let it steep in the refrigerator for about 4-5 hours and stir from time to time.
You can of course also use basil instead of parsley or in addition, but then no more than 3 teaspoons of each.