feat: version 4

[mdonnalley]

oclif testing utilities without fancy-test

Why?

We're migrating away from fancy-test for a few reasons:

• it assumes people will use mocha as their test runner
• there's a learning curve to writing fancy tests. Most people know how like to write their tests and don't want to bother with learning a new test framework
• fancy-test offers a lot of useful utilities (like stubbing process.env) but it doesn't do everything that people need so people end up writing tests that are half fancy-tests and half "unfancy" tests. We'd rather enable people to write tests however they want.
• we don't have bandwidth to support it as fully as we would like

Migration Guide

POC
oclif/plugin-not-found#632
oclif/oclif#1420

@W-15470644@

[cristiand391]

QA notes:

migrate fancy-test in https://github.com/oclif/plugin-commands
done here: oclif/plugin-commands#671

⚠️ migration guide example shows expect is exported by @oclif/test

some examples have import {expect, test} from '@oclif/test' but that fails saying expect isn't exported.
current major exported it from fancy-test:

test/src/index.ts

Line 41 in 8be535f

export {FancyTypes, expect} from 'fancy-test'

EDIT:
ignore my comment above, I misread the guide and thought the imports were in the after examples, checked again and everything looks good.