Move testing framework over to Jest

[AnujRNair]

Summary

This PR:

• Removes the Jasmine testing framework and replaces it with Jest.
• Updates the tests to use the new framework / runner
• Updates the tests to test in memory file system rather than writing to the physical filesystem
• Refactors the tests to organize them better and make them easier to work with.
• Updates the npm scripts to reflect the new changes

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've written tests to cover the new code and functionality included in this PR.
• I've read, agree to, and signed the Contributor License Agreement (CLA).

[codecov]

Codecov Report

Merging #24 into master will decrease coverage by 3.57%.
The diff coverage is 100%.

@@ Coverage Diff @@ ## master #24 +/- ## ========================================== - Coverage 97.32% 93.75% -3.58%  ========================================== Files 2 2 Lines 187 80 -107 Branches 14 11 -3 ========================================== - Hits 182 75 -107  + Misses 5 4 -1  - Partials 0 1 +1

Impacted Files	Coverage Δ
plugin.js	91.52% <100%> (-1.54%)	⬇️
test-utils/webpack-helpers.js	100% <100%> (ø)

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