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This pull request addresses https://github.com/matteosister/GitElephant/issues/55
Then in each DateTime use, you should set the timezone correctly. Overwriting a .ini parameter really shouldn't be the concern of the library (even if it is "only for the tests").

If you really care about this directive (rather than setting properly your php.ini setting, which is the way to go), you should test if this directive isn't set, and then set it if it is not the case.