How to test for specific potions in inventories? [duplicate]

I was helping my sister with her server commands when I got stumped on this. I want to find if the player has a specific potion with this:

/testfor @a[team=Sandwings] {Inventory:[{id:"minecraft:splash_potion"}]}

and this:

{Potion:"minecraft:poison"}

But I don't know how to combine them.