Add universal/consistent tests for loss modules

[njzjz]

+ Hits        42870    43087     +217     
- Misses       7822     7934     +112     
- Partials      946      948       +2     

I see that 1/3 of the new codes have not been tested.

Where can I see these datas about missing UT? I will add UT based on these datas.

You can click the link sent by @codecov or click the codecov checks.

It looks like the loss module is not tested. @iProzd Do we have a universal test fixture for loss functions?

Not yet, maybe we need a discussion to design a universal test for loss modules.

Originally posted by @iProzd in #3867 (comment)