For the black cherry tarragon shrub, pulse the ingredients together in a blender a couple of times until the cherries are chopped and pulpy. Empty the mixture into a bowl and cover with plastic wrap. Refrigerate overnight. Strain out the pulp and discard it, reserving the liquid. Distribute the liquid between clean mason jars. Screw on the caps and keep refrigerated until use. You can drink it as-is, or mixed with tonic water for a bit of carbonation, or mix it into cocktails.