Sure, you *can* keep all kinds of Tetras with Molly fish as they are "community fish", but only if you plan on not giving your Mollies the brackish water that really makes them thrive. Yes, people will say over and over again that Mollies *can* live in freshwater, but from their origins and from true Molly fish keepers, they will swear by Mollies living in brackish (semi-salt) water. I keep my Mollies in a brackish environment and they are much happier. It's their true and natural habitat and when you mix them in a community tank of other freshwater fish, historically they will not live as long and are more prone to sickness/disease.
Tetras should NOT be kept in brackish water. Salt in the water at low levels is actually not harmful to any tropical/community fish, but to go as high as brackish, it is not healthy for them.
Also, just please note (from my horrible experiences), if you mix Tetra in with other non-Tetra community fish (including Mollies if you do just decide to have the Mollies live in freshwater), if/when your tank gets an Ich outbreak, do NOT use Malachite Green to treat it (which is normally one of the best Ich meds) - it will kill your Tetra like that *snaps fingers* -- they are thin scaled and it will basically eat through their skin - sadly, I did not know this before hand and I killed my entire Tetra tank.
There are a LOT that are ok with tetras, in fact too many to name. Just hope you never have to deal with it. But if you do then just deal with the treatment for that specific illness as even then there will usually be several different medicines just to treat that single illness. For example, malachite green based meds can actually be used with tetras, however, you need to cut the dosage in half. I still would probably use a different medication, but it is "possible" to use it on tetras and have them live through the treatment.