test: migrate from test runner tap to jest

[petermetz]

Update 2021-08-09

This used to be about AVA but now is about Jest

Update 2020-11-02

Switched the target to AVA from jest, details below in comments.

Description

As a developer I want to be able to write unit tests for the universal packages that execute the same code both in NodeJS and in the browser so that I don't have to duplicate work in order to have test coverage for both platforms for the cross-platform packages.

While working on the stable signature generation, we've discovered that accidentally the wrong library was used initially (congratulations to Peter) which is called "tap" instead of "tape". They both do the same thing (test runners for TAP - Test Anything Protocol) but the tap library does not work in browsers while the tape library is, so to keep the build/test infrastructure of the project as simple as possible it would be the best to migrate to tape entirely since it anyway has support for TAP (the protocol)

https://www.npmjs.com/package/ava

Acceptance Criteria

1. Complexity of build/test scripts has not increased
2. Tests for cross-platform packages such as cactus-common can be written once and ran "anywhere" (NodeJS, browser)
3. Developer workflow has not lengthened, did not increase in complexity (from the human perspective, not code-wise that was mentioned in 1))

cc: @takeutak @sfuji822 @hartm @jonathan-m-hamilton @AzaharaC @jordigiam @kikoncuo

[petermetz]

Good news discovered in the meantime: Since both tap and tape use the Test Anything Protocol under the hood, they can actually run each other's test cases without issues. E.g. you can do npx tap some-test-case.test.ts and if will "just work" regardless of the test case being written with tap or tape.
This is good news because it means we can gradually perform the migration without any sort of unstable transition required.

[petermetz]

Refactoring this as per #299 (comment) to be about migrating to AVA not tape...