Migrate testing from enzyme to @shopify/react-testing

[BPScott]

Polaris-react has two ways of running tests:

• The modern way: import {mountWithApp} from 'test-utilities' which uses @shopify/react-testing per this file.
• The legacy way: import {mountWithAppProvider} from 'test-utilities/legacy' which uses enzyme per this file.

In order to simplify our testing story and only have one way of doing things we should remove all usage of enzyme and test-utilities/legacy, cumulating in removing src/test-utilities/legacy.tsx and all enzyme dependencies.

In order to do this however we need to migrate all the tests that currently use test-utilities/legacy. That's where you come in.

1 Migrating tests

• Search the codebase for test-utilities/legacy to find imports of that file.
• Replace import {mountWithAppProvider} from 'test-utilities/legacy' with import {mountWithApp} from 'test-utilities' and migrate the test content so it passes
• TODO there's probably some docs from "how to to migrate from enzyme to react-testing" that came out of doing this work in web. Hunt them down and link them here.

@vsumner had some codemods that helped auto migrating the web codebase they might cover a lot of use cases

2 Remove foundations

• Delete src/test-utilities/legacy.tsx
• Remove any mentions of enzyme in tests/setup and anywhere else in the codebase
• Remove enzyme / enzyme-adapter-react-16 dependencies from package.json

[vsumner]

The codemods that I started and have been expanded on by web-essentials could easily be ported for this: https://github.com/Shopify/web/tree/master/packages/%40shopify/codemods

[BPScott]

Migration was completed and enzyme was removed in #4432 🎉