Improving Test Coverage for the TARDIS Plasma Module

The plasma module is used to determine the ionization and excitation states of the supernova ejecta using the basic structure of the supernova (elemental abundances, densities, radiation temperature). As described in the project description in the GSOC project page, CodeCov does not accurately report coverage of the TARDIS plasma. This is because the plasma module is used as a parameter for models and simulations, and is therefore indirectly tested by the tests of the simulation and model functions. While there are parts of the plasma module that are tested directly, many aspects of the module have no easy to find direct tests. This project aims to increase the test coverage of the plasma module and make the tests of the plasma modules easy to find and read.