When using a negative amount, an invalid solution can be reached and chosen for output, hitting an assertion when trying to format the solution:

vroom: ./utils/helpers.h:196: vroom::Solution vroom::utils::format_solution(const vroom::Input&, const RawSolution&): Assertion `amount <= v.capacity' failed.

This happens because during the local search there is no validity check wrt capacity for removing a job from a route. But removing a job can break the capacity restrictions if it holds a negative amount.

The rationale behind capacity values being signed integers is that I was thinking this could be useful to model some pick-up and drop-off situations. I'd like to keep this as is, so the fix would be to add validity checks for capacity to all local search operators upon job removals.

Note : using current master or v1.3.0 with positive values only for capacities is safe from this bug.