Learn Portuguese (Portugal): Eles não têm saudades dos testes, pois não?

Because the main sentence is a negative statement (Eles não têm...). In Portuguese, when you want to ask for confirmation after a negative sentence, you use the tag pois não?. If the sentence were positive, you would use não é?.

Why is the verb têm used to say they miss something?

In Portuguese, missing someone or something isn't an action you do, it's a feeling you have. You use the verb ter (to have) followed by the plural noun saudades (a feeling of longing) to express this.

Why does têm have a circumflex accent on the 'e'?

The accent marks the plural form of the verb. tem without the accent means he, she, or it has, while têm with the accent means they have.

What makes up the word dos before testes?

The phrase ter saudades must be followed by the preposition de. Because testes is a masculine plural noun, we also need the word for the, which is os. Combining de and os gives us dos.