Add more tests for the material state

@samuelpmishLLNL mentioned that there weren't a lot of tests here. This should be shored up.

Start by locating the material state implementation and any existing tests in the repository, since the issue names no files or test entry points. Determine which material-state behaviors lack coverage, then add focused tests and run the relevant test suite to confirm they pass.

Written by the indexing model from the issue text.