More tests to improve coverage

[charleskawczynski]

Based on RRTMGP.jl's coverage, the lowest coverage comes from

• mo_fluxes_byband_kernels, with the Julia counter part coverage here
• mo_optical_props_kernels, with Julia counter part coverage here

It might be nice to add examples that touch more of these kernels.

[RobertPincus]

@charleskawczynski Thanks for the suggestion. In fact I was just putting together a list of things I'd like to include in coverage testing. This will likely be a separate repo.

[RobertPincus]

@charleskawczynski This issue motivated the new regression tests in commit e68ad73. See tests/ directory. I hope to figure out a way to integrate code coverage into the continuous integration automatically.

[charleskawczynski]

Looks good!