Replace expect with assert

[bgins]

Summary

This PR implements the following features:

• Replace expect with assert

The PR replaces expect with assert to make browser testing easier. expect relies on node APIs while assert does not.

We will add browser testing in a future PR.

Test plan (required)

Run npm test. All tests should pass like before.

Closing issues

Closes #540

After Merge

• Does this change invalidate any docs or tutorials? No
• Does this change require a release to be made? No

[icidasset]