Establish guidelines for writing Jest tests

[Silvyre]

Presently, across all merged and pending test files, an assortment of testing syntax is used, and few structural similarities exist. For example, some testing files use describe(), while others do not; some tests use test(), while others use its alias it(), etc.

I feel that it would be helpful to Telescope's future maintainers if we established and started abiding by some common conventions or guidelines for writing test files. This would first require us to determine our preferred coding style for test files, including which pieces of Jest syntax each testing file should or should not utilize.

[miggs125]

This is a great idea!. We should do this in the CONTRIBUTING file

[humphd]

See #245, which has some excellent sample code for doing mock network requests in tests.

[humphd]

cc @manekenpix, who has written a bunch of our test code.

[humphd]

https://devhints.io/jest is really useful, we should link to it somehow in our docs.

[c3ho]

Closing this issue as it is too vague.