various issues with unit tests

[ismael-mendoza]

I find that unit tests are very redundant and hard to reproduce, in particular some of them are breaking even though the images and the corresponding code is still the same. It's really hard to figure out why though

In general, I'm not sure if we should include scarlet/sep/lsst in the unit tests. I feel that correctness of the images produced should be independent of the algorithms for detection.

I think the testing suite needs an overhaul in terms of deciding whether each test is should actually be included. Here is a list of things that I'm debating whether we should include in the testing suite at all:

• whether detection works by various algorithms like sep/scarlet/lsst

• group sampling functions from WeakLensingDeblending (these seems like an additional feature to define realistic groups, but maybe we should move away from depending on descwl and definite our own groups as suggested in Implement friends-of-friends algorithm to generate blends #16)

• most of the config tests are broken, these need to be revived at the same time as btk_input is broken and cannot be currently used  #48 (they are more broken now than before because of definite our own Survey objects instead of a string)

• Tests should not depend on band order which can be easily switched (architecture in general should use dictionaries for bands?)