add tests for DynamicMatrix

[ibaned]

commit a1f17cc makes it pretty clear that code isn't tested. this issue is something we can have an undergrad / work study do, so low priority but keep it in mind.

[wrtobin]

I haven't checked but do we do any coverage analysis?

In my thinking, that would be a good place to start for someone assigned to this issue.

[ibaned]

nope no coverage being done right now. CMake and friends should have some integration with that though, and we could put up results the same way we put up documentation. I made that a separate issue, #60