Sometimes I wish the @INC paths had "same directory as the main script" option!

I think I've done something like this before. The following is untested:

BEGIN {
  use File::Basename;
  my $dir = dirname(__FILE__);
  unshift @INC, $dir;
  require MyModule;
}
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If your module has functions, you can just use the whole package/function name to refer to them in your test, e.g. MyModule::function(@args), or explicitly call MyModule->import after the require. This way, I can run the tests from any directory, even from outside of the whole build directory.