Cleanup: allow runtime logs in unit tests

[BlaineEXE]

Enhancement

Why is this needed?:

While there are different philosophies for logging in unit tests, it can be helpful to see examples of runtime log output in unit tests.

Describe the solution you'd like in detail:

For COSI's unit tests, the quickest and likely best way to implement this is using testr.New as suggested by @shanduur .

Describe alternatives you've considered:

Currently, no runtime logging is shown in unit tests, which is the other alternative.

Additional context:

Original discussion: #170 (comment)

[BlaineEXE]

Personally, I am in favor of this. We could discuss whether there are ways to optionally enable/disable this, but I would leave that for the future if someone asks for it.

Log outputs don't usually need strict unit testing, but it is important for developers to be able to get an idea of what logs will be shown during runtime so we can assess how debuggable system errors will be. For community-contributed PRs, being able to see the output logs in unit tests will mean we don't need to deploy COSI to see an example of runtime logs.