Use msw instead of fetch-mock to test fetch in browser

[trivikr]

Is your feature request related to a problem? Please describe.
The issue which returns null response body for null body status is not reproducible with fetch-mock in #5

It's likely because fetch-mock doesn't create actual fetch call to a local server, and mocks fetch behavior.
Docs: https://www.wheresrhys.co.uk/fetch-mock/

Describe the solution you'd like
Use mock service worker to create a server to which fetch call can be made to https://www.npmjs.com/package/msw
The previous attempt was made in #1

Describe alternatives you've considered
N/A