Adding more TF2 level 1 (and one level 2 API) API tests

[tatianacv]

Fixes #221.

Commits

• [x] I slowed down and took a deep breadth 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.

Expectations

This PR contains tests that verify that we are able to process different TF2 level 1 APIs and one TF2 level 2 API (random.uniform). These tests are in the https://github.com/ponder-lab/ML, and this PR verifies that they also pass in this project.

Testing

• [ ] 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.

Tests for:

1. Variable
2. Tensor
3. ones
4. fill
5. zeros
6. zeros_like
7. one_hot
8. eye
9. constant
10. convert_to_tensor
11. range
12. random.uniform

Final Checks

• [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.