modifications made by agilgur5 to brekk's original commit:
- rebase with `master` that is 3 years newer
  - fix conflicts with newer code, esp the `tsModule`/`tsProxy` changes
    in this commit
- move `jest` config to the bottom and don't reformat `package.json`
  with tabs

modifications made by agilgur5 to brekk's original commit:
- fix merge conflicts with code that is 3 years newer

- and ts-jest to v28
- @types/jest doesn't have a v28 yet

- look ma, no more vulns!

- and add JSDoc typings to it
  - per https://jestjs.io/docs/configuration

- most of these options are either unused (like `modulePaths` etc) or
  covered by Jest's defaults (`moduleFileExtensions`, `testMatch`, etc)

- also use `ts-jest` preset per its docs and migration docs
  - https://kulshekhar.github.io/ts-jest/docs/migration

- per ezolenko's request, though I also prefer to separate them

- fix all relative imports to use `../src/` now

formatting changes:
- improve ordering of imports in tests -- externals first, newline, then
  internal imports
  - do this **consistently**
- consistently put spaces around braces in destructured imports
  - really need better linting (and update to ESLint)
- consistently add newline after imports and before declarations

- in general, add more newlines for readability in several files

- no config needed and uses standard imports too
  - also required for future Jest ESM support I believe
  - I created the `jest-without-globals` package before this feature was
    released in Jest core and contributed a PR for it too, so might have
    a bias toward not using globals

- basically to match the changes I made when fixing declaration map
  sources ~1.5 years ago in ec0568b
- also to add `cwd` to options

- fix: use `toStrictEqual` everywhere, in order to actually check
  `undefined` properties, as this is necessary for some of the checks
  - I believe the original author may have intended to actually check
    `undefined` given that they wrote it in the test, but maybe did not
    know to use `toStrictEqual` instead of `toEqual`

- instead of re-writing the options multiple times, write up some
  defaults and use object spread
  - and refactor `makeDefaultConfig()` to just use
    `{ ...defaultConfig }` instead to match the rest

- re-write normalizePaths to be a `for ... of` loop instead of using
  `Array.map`
  - simpler / more straightforward than a function with side-effects

- feat: add typings in several places
  - that's why we're using TS and ts-jest right??

- LanguageServiceHost now requires 3rd argument, cwd, so add that to
  all usage
- add afterDecalarations to transformers

- Jest's test.skip can now use async/await, so do that
  - it was also giving a type error, and this is simpler anyway

- change expected to use `__tests__` directory now

- fix: use `expect.arrayContaining` for `host.getDirectories` test as
  there are more temp directories that get added here, such as
  `build-self` and `coverage`
  - in general, might be less fragile if this used a generated directory
    instead of an actual one
    - but save bigger refactors for later

- instead of using Promises with `done()`, use async/await for clearer
  code and less indentation too

- remove the `truncateName` function as it's not needed; `local` will
  result in the same name

- remove commented out test code
  - this seemed to just be there for testing the code, and not
    ready-for-production comments

- basically using pre-defined fixture vars instead of ones defined
  inside the test
  - which is more straightforward, easier to read, and less fragile
  - shorter names too

- also use a __temp dir for auto-generated files instead of creating
  them in the same dir and confusing the editor file tree and potential
  watchers
  - change jest config to make sure only spec files are being watched
  - gitignore __tests__/__temp/ dir in case tests crash etc

- use PluginContext and IContext types instead of `any`
  - we're using TypeScript right??
  - add `debug` level logging in a few places where it was missing

- update stubbedContext to have latest PluginContext properties
  - watcher isn't in there anymore and a few new properties were added
- fix type errors with stubbedContext
  - give it an intersection with IContext for `info` and `debug`
    verbosity levels
  - force the logging funcs to `any` as they don't quite match the
    Rollup types
  - force them to `any` when deleting them as well because they're not
    optional properties

- Note: would be good to not force so much `any` if possible, but this
  may be difficult without more advanced internal Rollup mocks
  - couldn't find any testing packages for this :/

- test: add verbosity expect for debug too
- refactor: context2 -> context
  - there wasn't another one, so just use the same name consistently
    - I'm guessing there was another one at some point in the
      development of this and then it was removed but not renamed

- surprisingly only in jest.config.js?

- really need to update to @typescript-eslint ...

- run after all the builds for now
  - it can be done in parallel as a separate job, but then have to
    duplicate the NPM install etc, so may not be optimal that way

- refactor: add test:watch and test:coverage scripts
  - shortcut scripts so don't have to `npm test -- --coverage" etc
  - also remove `--verbose` from `test` as that's not necessary

- increases coverage of get-options-overrides significantly
- couldn't figure out `rootDirs` -- either the code or my tests are
  wrong, so just skip that one for now

- refactor: move makeStubbedContext etc into a shared fixtures dir so
  that it can be used for both rollupcontext tests _and_
  createFilter tests
  - in my stylistic opinion, I prefer to put nearly _all_ consts like
    these into fixtures dir
  - configure jest to ignore test helpers in coverage reporting such as
    fixture files

- format: '' -> "", add semicolon in some places
  - I use single quotes and no semicolons, so missed that in a few
    places
    - lint didn't check for that and no prettier auto-format :/

- basically using pre-defined fixture vars instead of ones defined
  inside the test
  - which is more straightforward, easier to read, and less fragile
  - shorter names too
  - left a couple of ones as is where they were only used once very
    quickly -- could make them fixture vars too but 🤷

- use async/await instead of Promises with `done()` etc
- also use more `fs-extra` functions that support Promises instead of
  synchronous `fs` functions (e.g. `existsSync` -> `pathExists`)
  - async should be a small optimization for tests too

- fix: use __temp dir for auto-generated files instead of creating
  them in a fixtures dir and breaking actual fixtures

- format: a few multi-line statements were able to be condensed to a
  single line, so do so
  - esp as multi-line was not helping readability since this is just
    irrelevant test data (may have hampered readability actually)

- goes over the different ways of running the tests (watch + coverage)
- line about unit and integration tests was moved into this section
  - and altered to reflect the current state of the repo now that a good
    amount of unit tests exist

- also move "Linting and Style" into its own section with a list
- move "fix any failed PR checks" to the top as overall guidance on
  making a PR
  - previously it was in the middle of linting and style, which felt a
    bit disjointed (maybe made sense earlier before builds were in CI?)

- name the last section "Building and Self-Build"; leave content as is
  - well mostly, change the first line as "fastest way to test" is not
    necessarily accurate anymore now that there are actual tests

- original author, brekk, had made these changes, likely because without
  them, the tests would throw in the source lines where `tsModule` was
  used with things like "Cannot read property 'ModuleKind' of undefined"
  - the actual fix for this is to instead use `setTypescriptModule` from
    tsproxy as this is how it is used in the source
    - it's mainly needed for when an alternate TS is substituted
    - brekk probably didn't know the codebase well enough to know that
    - add `setTypescriptModule` to all specs that need it

- 100% test coverage of tsproxy now too!

- this should hopefully fix the build errors we were getting as well

- it seemed incomplete and that's why it was skipped, no comment there
  stating otherwise, so just modified it a bit to get it to work and
  pass properly

- drop Node 10 testing
  - Node 10 went EoL a while ago and was causing the latest version of
    Jest to throw an error
- still test Node 12 since it only went EoL recently, but could drop it
  as well if wanted
  - may want to set `package.json#engines` or update min requirements in
    the README if so, though it likely still works on older Node, we
    just can't easily test it

- add macOS and Windows testing to the matrix since TS and Rollup both
  behave differently on different OSes, in particular with regard to the
  filesystem
  - POSIX paths on Windows, case-insensitivity on macOS

- give the job a name that appears in the PR checks and Actions tab

- similar to previous commits, don't use the actual fixtures dir, use
  the `__temp` dir and a subfolder within for this spec file
  specifically so as to not interfere with other tests

- test: get the skipped `readFile` test to work
  - `ts.sys.readFile` definitely returns stuff, it's used for snapshots
  - it wasn't working because it was testing the wrong extension,
    `.js` instead of `.ts`
    - I thought this was intentional when I first added consts here, but
      turns out that was actually a mistake by the original author
- refactor: merge the `readFile` tests with the main test suite
  - first I merged them together, but as they were just one-liners, I
    merged them with the first set, since it wasn't particularly
    different from those

- refactor: split up the main test suite into a few commented sections
  - core snapshot functionality, fs functionality, misc
  - a lot less random now
- refactor: use `getDirectories` on the testDir instead of project root
  - much less fragile to use the dir generated here, and no hack-ish
    `arrayContaining()` either
- refactor: one-line the case-insensitive test
  - that simplifies it a lot!
- refactor: use fixed consts for the repetitive default config
  - and use a `testOpts` variable for less fragile testing

- test: add tests for version 2 branches of snapshot funcs
  - these weren't tested before so it had only tested the `|| 0` branch
    of the conditional
  - also actually test `reset` instead of calling it at the beginning
- refactor: no more "dirty checking" of instances' private interfaces
  - we're testing it all through the public interfaces instead!

- test: add a simple test for the new `trace` method

- test: coverage for `after` and `afterDeclarations` transformers
- test: coverage for different `undefined` states of transformers
  - refactor the two test suites as one for `undefined` and one for
    all 3 transformers
  - and put the working one first for naming purposes
  - refactor the `setLanguageService` call as a simpler type coercion
  - remove the transformer interactions in the main test suite

- yea, this is a big commit, but I was refactoring everything anyway and
  this is probably gonna be squashed anyway

- no need to check private interfaces in these remaining tests, the
  functionality itself is already tested via the public interface

- host is only case-sensitive on Linux
  - prev was everything except Windows; so flipped the conditional a bit
- host and TS itself use "/" normalized paths, so use those
  - and add a hacky workaround for a TS bug I managed to find

- formatHost will use OS separators, so no "/"
  - make the test more accurate and less fragile by comparing to
    `process.cwd()` as well -- which should normalize on Windows

- think it's a bit easier to read this way, it's only 3 tests after all

- this isn't necessary and added some complexity (and verbosity)
  - only one dir that needs normalization anymore, and that's just the
    cache dir, so just add it to the const/var fixture instead

- shrink the code a bit as a result too
  - and use a bit different code style to shrink it too

- annnd found a Windows bug in get-options-overrides.ts here too...
  - leave a `// TODO: ` comment here to fix the source as this PR is
    solely focused on tests (i.e. no source changes)