Will I ever 'test out' of certain skills-- even my 'basic' ones continue to show up as colored again but I feel like I totally have those down and I don't want to keep going back to them.
Keep on practicing and learning and you will have a Duo trophy and a golden tree to be proud of, not a broken tree and lousy strength bars.
Testing out is for lessons that you don't want to complete because you already know the skills.
What you're seeing is Duolongo's spaced repetition approach. It shows you things you've learned at times that will most help them stick in your head. If you keep the tree gold, you'll find it works really well. Sometimes that means you don't make any progress through the tree for a while - that's fine.
Duolingo takes account of how long it takes you to answer the question, and it takes account of whether or not you "peek" - whether or not you hold the mouse over a word to see what it means. When you can answer the questions quickly and without peeking, the skills will decay more slowly.
After you've strengthened the skills a few times, they'll start decaying more slowly, and then you'll be able to get further through the tree.
Even swimming within our own language very often we have to peek and dive into our brain let alone with a different language. For a few seconds? Quite often I peek to see "what Duolingo prefers". Duolingo has a certain bent to adopt very geometrical or formal phrase constructions. Allowances are made for some typos though for others it seems somehow funny because I believe no one in his right mind would make them. And they are dubbed as errors. But on the whole, the system is extremely well thought of. The iterative process of hammering on certain phrases and jumping between two languages is useful. You are quite right.