Direct way to test hypothesis? The standard procedure for the hypothesis testing is that we state the null hypothesis and the alternative, and then we see if we can reject the null hypothesis.
Then, if we can reject the null hypothesis, we accept the alternative.
In my class, the professor explained the similarity between this argument and the proof by contradiction.
Now I got the question: in mathematics, we can prove theorems directly, not just by contradiction.
So, is there a way to “directly” test the validity of a hypothesis?
I am pretty sure this has been asked elsewhere, but I could not find the duplicate.

As pointed out in the comments, Bayesian inference would be a way to "pile up" evidence in favour of a hypothesis. This, however, would always fall short of a proof.
I think an important point to bear in mind is that a single counterexample can
establish that a claim is false, while no amount of evidence can establish that a claim is right; hence, using evidence alone we can reject hypothesis, not establish their validity.
Edit: On re-reading your question I have a minor comment: you say "...if we can reject the null hypothesis, we accept the alternative."
This is not necessarily the case. The evidence can be in strong disagreement with the null, and in still stronger disagreement with the alternative. This would force you to re-think your problem, and enlarge either the null or the alternative, as seemingly neither one  provides an adequate model for your observations.
