  Autonomous cars are subjected to several different kind of inputs (other
cars, road structure, etc.) and, therefore, testing the car under all possible
conditions is impossible. To tackle this problem, scenario-based testing for
automated driving defines categories of different scenarios that should be
covered. Although this kind of coverage is a necessary condition, it still does
not guarantee that any possible behaviour of the autonomous car is tested. In
this paper, we consider the path planner of an autonomous car that decides, at
each timestep, the short-term path to follow in the next few seconds; such
decision is done by using a weighted cost function that considers different
aspects (safety, comfort, etc.). In order to assess whether all the possible
decisions that can be taken by the path planner are covered by a given test
suite T, we propose a mutation-based approach that mutates the weights of the
cost function and then checks if at least one scenario of T kills the mutant.
Preliminary experiments on a manually designed test suite show that some
weights are easier to cover as they consider aspects that more likely occur in
a scenario, and that more complicated scenarios (that generate more complex
paths) are those that allow to cover more weights.
