Tests_solutions: Tests calls step with illegal action

[DominikRoB]

Still investigating the legal and illegal actions.. (:

I noticed that the following code in test_solutions.py does not check for illegal actions:

            if no_op and not done:
                self.assertTrue(len(env.next_time_step) > 0, "step {}".format(step_nb))
                previous_time_step = env.current_time_step
                state, reward, done, _ = env.step(env.jobs)
                self.assertTrue(env.current_time_step > previous_time_step, "we increase the time step")

But sometimes the nope-action is not legal when getting used.

Not sure if its an issue with the test design or if there is a risk that the agent can't reproduce the solutions on its own.