On Fri, Nov 25, 2016 at 06:41:23PM +0100, Johannes Schindelin wrote: > > Ah, I didn't realize that was a requirement. If this is going to be part > > of a release and real end-users are going to see it, that does make me > > think the config option is the better path (than the presence of some > > file), as it's our standard way of tweaking run-time behavior. > > So how do you easily switch back and forth between testing the old vs the > new difftool via the test suite? If it's for a specific tool, I'd consider teaching the test suite to run the whole script twice: once with the flag set and once without. That is sometimes more complicated, though, if the script creates many sub-repos. An environment variable might be more natural. If you already support flipping the default via config, you can probably do: GIT_CONFIG_PARAMETERS="'difftool.usebuiltin=true'" export GIT_CONFIG_PARAMETERS -Peff