tests/test_advanced_image_processing.py: Added a test for merging two neurons with advanced_image_processing.postprocess_data using 3D data.
tests/test_advanced_image_processing.py: Added a test for merging two neurons with advanced_image_processing.postprocess_data using 3D data.

nanshe-org/nanshe,jakirkham/nanshe,DudLab/nanshe,nanshe-org/nanshe,jakirkham/nanshe,DudLab/nanshe