Units Tests for Route plan

[hjabbot]

Moving here from project repo #160

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There's quite a lot of edge cases which cause the Route Planner to crash, such as attempting to route plan without currents in the mesh or attempting to navigate to an inaccessible waypoint. These should be captured in Units whenever they are found so we can ensure they are fixed as part of the 0.3.x release

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Adding notes here for some units tests to create:

* The Route Planner crashes in un-informative ways when run using a misformatted config file.

* The Route Planner crashes when attempting to navigate to a point which is on the boundary of a mesh

* The Route Planner crashes when attempting to navigate to a waypoint which is in an inaccessible cellbox

* The Route Planner crashes when attempting to find a route in a mesh which does not contain a vector field

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This seems messy but important to do before the refactor is folded in

[gecoombs]

My understanding is that the issues listed above are now fixed, especially with the refactored version of the route planner. Are you happy to close this issue, either now or on merge of 0.6.x? @hjabbot @SamuelHall700

[hjabbot]

:+1: Either way is fine by me