Increase code coverage

[dantownsend]

Now we have codecov integrated, it's easier to track code coverage.

There are some areas of the code base which require additional testing.

[aminalaee]

@dantownsend Can this be closed?

[dantownsend]

@aminalaee Yes, I can close it.

Looking at the coverage now, it's much better - thanks for that.

Only minor bits of coverage are missing now, and I can create separate issues for those.