Testing strategy outdated

[hjabbot]

The testing strategy is a bit confusing at the moment. We need to put a set of test files to run through for each file mentioned in them to avoid missing regression tests when putting in PRs.

e.g.
This table means that test_routes_dijkstra.py and test_routes_smoothed.py should both be run in the case that any of crossing.py, crossing_smoothing.py, or route_planner.py are altered, but instead it looks like no test should be run for route_planner.py being altered.

Route Planning

Files altered	Tests
crossing.py	tests/regression_tests/test_routes_dijkstra.py
crossing_smoothing.py	tests/regression_tests/test_routes_smoothed.py
route_planner.py

Also just a personal opinion: I am constantly forgetting that testing_strategy.md in the tests folder rather than the .github folder when I'm looking up what tests to run. Anyone else have this issue? If so I suggest moving it to .github for consistency's sake.