error no longer accepts arbitrary class constructors

error (aka throws) no longer accepts arbitrary class constructors. Any provided class constructor must extend Error, e.g. built-ins like SyntaxError or custom error classes like class MyError extends Error. Thanks to the nature of JavaScript, providing a class constructor that does not extend Error will lead to undefined behavior.
error only captures exceptions from Babel

error (aka throws) no longer potentially captures exceptions thrown by the formatResult function. If the formatResult function throws, the entire test will fail immediately.
TypeError for config error; AssertionError for test error

All configuration-related issues now throw TypeError instead of AssertionError. AssertionError is now exclusively used for failing tests. Additionally, the text of some error messages has been updated.
All test titles are now numbered

All test titles are now numbered (e.g. "1. ...", "2. ...", etc), including fixtures tests and tests with custom titles.
Built-in TypeScript support

TypeScript types are now included within the package itself, obviating the need to install a separate types package. Installing the old types package alongside this version of babel-plugin-tester will cause conflicts.
Fixture configuration schema is standardized

In previous versions of babel-plugin-tester, you could provide any key to options.json and it would be passed as-is to the plugin under test. This made it impossible to allow fixtures to be configured with the same flexibility as test objects. In this version of babel-plugin-tester, fixture options.json (and options.js) files must return a standard set of options. Non-standard properties are silently ignored. For instance: to pass options to the plugin under test, they must be provided via pluginOptions.
Global describe and it functions must be defined

babel-plugin-tester will refuse to run if describe, it, it.only, or it.skip are not globally available.
Global setup/teardown no longer overwrites local versions

In previous versions of babel-plugin-tester, test-level setup and teardown functions overrode global setup and teardown functions. In this version of babel-plugin-tester, the global setup and teardown functions will be called alongside their test-level counterparts for each test and in a well-defined order (see documentation).
Implicit "global" options merging is no longer supported

In previous versions of babel-plugin-tester, any test object and fixture configuration option could be passed directly to babel-plugin-tester and apply "globally" across all test objects and fixtures. This was even the case for options that made no sense in a "global" context, such as only, skip, and code. In this version of babel-plugin-tester, only options explicitly listed in the documentation can be passed directly and applied globally. Unrecognized "rest" options are silently ignored.
Test/fixture configuration is resolved early and consistently

In previous versions of babel-plugin-tester, test object and fixture configuration options were resolved in various places, with some options getting finalized before it(...) and describe(...) were called and others being determined as Jest was executing the test. In this version, all configuration options are resolved and finalized before it(...) and describe(...) are called. This also means configurations are finalized before hooks like beforeAll get called by the testing framework.
babelOptions.filename is now set to filepath by default rather than undefined.
In previous versions, the lodash.mergeWith customizer skipped source properties that resolved to undefined. With this version, the customizer now unsets these properties (sets them to undefined), allowing the end user to easily unset defaults (e.g. filename).
Minimum recommended node version bumped from 10.13.0 to 14.20.0
Plugin names are once again automatically determined by analyzing the return value of the plugin function. Though this is implemented in a backwards-compatible way, there is a [small caveat][15].

✨ Features

Add support for testing presets ([73b90b3][16])
Implement default filepath inference using Error stack trace ([9d1b321][17])
src: add exec/execFixture support via Node's VM module ([4754f42][18])
src: add support for "only", "skip", and "title" test options in fixtures ([#90][19]) ([89b58b5][20])
src: add support for arbitrary run order of plugin under test ([#91][21]) ([8c8b858][22])
src: add support for loading prettier configuration files in fixtures ([f54deda][23])
src: add TEST_SKIP/TEST_NUM_SKIP/TEST_ONLY/TEST_NUM_ONLY env variable support ([13626d1][24])
src: bring back (lightweight) plugin name inference ([#92][25]) ([f9ad903][26])
src: implement titleNumbering and restartTitleNumbering options ([09e792d][27])
src: implement standard setup/teardown run order ([4ea283f][28])
src: provide debug output support via debug package ([4c7c6e7][29])
Windows support ([f214995][30])

🪄 Fixes

src: ensure test function errors are not swallowed by teardown function errors ([2acfe37][31])
src: fix fixtureOutputExt being ignored in root options.json ([#89][32]) ([481be19][33])
src: fix plugin run order for fixtures to match tests ([#88][34]) ([fbb6c19][35])

⚙️ Build System

deps: bump prettier from 2.8.0 to 2.8.1 ([#98][36]) ([0bdb351][37])
package: restore @babel/core@7.11.6 as minimum supported version ([00712c0][38])
Transmute codebase to TypeScript ([#96][39]) ([5f588e9][40])
Update tooling ([d5b4d9c][41])

🔥 Reverted

"test: make debugging names shorter and sweeter" ([0b869bb][42])

🧙🏿 Refactored

Lodash.mergeWith customizer now allows unsetting options by setting them to undefined ([74af680][43])
Reorganize source into unified extensible tester pipeline w/ first-class fixtures support ([0c44392][44])