Adding single-level TF2 API tests

Fixes #221.

Commits

[x] I slowed down and took a deep breath before committing. Otherwise, I will start a pristine branch and reissue this pull request.
[x] Before committing my changes, I checked my working directory carefully. I only staged the changes I wanted and ensured it was of the utmost quality.
[x] I used git diff and git status to check my work carefully before committing.
[x] I completely understand what I am committing and why.
[x] I completely understand why things are the way they are.
[x] The change I am proposing makes complete sense to me.
[x] For the most part, the changes in this pull request correspond to the problem or task I am solving or performing. In other words, only the changes that are supposed to be there are the ones included in this pull request.

[ ] If this is a bug fix, I was able to reproduce the problem locally before I made any changes (can use git stash to temporarily reset the working directory).
[ ] When I made (or put back) my changes, the problem I reproduced above was fixed.

[x] The changes I am proposing meet the expectations I have described above.
[x] I have performed a self-review of my code.
[x] I have commented my code, particularly in hard-to-understand areas.
[x] I have made corresponding changes to the documentation if applicable.
[x] I have added tests that prove my fix is effective or that my feature works if applicable.
[x] New and existing unit tests pass locally with my changes.