class ActiveSupport::TestCase

end
end
# create databases
parallelize_setup do
class ActiveSupport::TestCase

In your +test_helper.rb+ add the following:

Note: this feature is not available with the threaded parallelization.

but before the tests run.
databases or any behavior that needs to be run after the process is forked
Set up hook for parallel testing. This can be used if you have multiple

def parallelize_setup(&block)
  ActiveSupport::Testing::Parallelization.after_fork_hook(&block)
end