IPPM: Is hemisphere merging done correctly?

[caiw]

Hemisphere merging code currently looks like this:

for func, spike in spikes.items():
    extracted_spikes = spike.right_best_pairings if self._hemi == HEMI_RIGHT else spike.left_best_pairings
    if self._should_merge_hemis:
        other_hemi_spikes = spike.left_best_pairings if self._hemi == HEMI_LEFT else spike.right_best_pairings
        extracted_spikes.extend(other_hemi_spikes)

Shouldn't it be

#                                                                         v
        other_hemi_spikes = spike.left_best_pairings if self._hemi == HEMI_RIGHT else spike.right_best_pairings

since it's selecting the other hemisphere's pairings?

I've tried making this change, but then some tests fail (see #439) :/

[caiw]

I'm mainly hoping to make sure the tests are correct so I can use them for the #391 refactor