Add generic way to override general.yml config in tests

[chrismytton]

Currently the tests depend on certain settings in conf/general.yml being correct before they will pass.

It would be good if we could have a generic method that allowed you to override certain parts of the config within the tests. There is already a more specific version of this in the Zurich cobrand's tests.

It would potentially work something like (pseudo-code):

override_config MAPIT_TYPES => [ 'O01' ] {
  # MAPIT_TYPES is overridden for the duration of this code block
}

Relevant IRC discussion with @evdb

If you were happy to touch the code in commonlib you could add a method that let you override the config for tests. It could use the scoping so that when the guard object falls out of scope the config is restored.

and

The config can come from two places - the commonlib stuff, and FixMyStreet.pm direct.

[dracos]

I'd certainly rather leave mySociety::Config alone to simply read in the config as it does (so no need to touch commonlib), and for everywhere in the code to use FixMyStreet->config (currently 36 mySociety::Config in perllib, 52 FixMyStreet->config, so it'll presumably just be hangovers and should be easy to swap). Then a generic override would only be needed in the FixMyStreet test code and presumably could be based on that Zurich code.

[dracos]

Done in 94ac7786132a538a5742ba325eb7fe9eff89cfc9. Called by (actual code):

FixMyStreet::override_config {
    MAPIT_TYPES => [ 'O01' ]
}, sub {
    # ... code ...
};