Markov can be used to build trading models - here's a link to a short description.
https://www.quantopian.com/posts/inferring-latent-states-using-a-gaussian-hidden-markov-model
It's simply a "chain" of events where the events themselves may or may not be known but an outcome can be predicted in the current state. Speech recognition, computer learning are familiar areas which employ Markov chains.
In any case, backtesting is still crucial to understand something about your idea. For instance, if you're trading the opening price under "x" conditions, you want to have a good understanding that "x" conditions show up enough times to be profitable. That's the essence of a backtest.