Set up AVA for end-to-end tests

[NSeydoux]

This is an experiment to see what our end-to-end tests would look like written with AVA. The main reason we would consider changing test frameworks for the end-to-end test is due to the discrepency between the Jest Node environment and the actual Node environment, leading to some subtle and painful-to-debug issues.

A couple of obesrvations:

• If running the tests in a loop, the test titles must change at each iteration. This will no longer be an issue when the environment will be set by the test matrix.
• AVA encourages to break tests into smaller files rather than in subtests with "describe" statements.
• The tests are recompiled when ran, to avoid running stale tests.
• TS support is quite good: the transliped code runs the tests, but errors are reported in the TS source.

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[matthieubosquet]

I have a vague idea that AVA is better for integration tests and that Jest's node environment has slight differences with node.

But do we have a more specific list of differences between AVA and Jest that would make the decision to move to AVA for e2e tests easier?

[NSeydoux]

Not a list of differences between AVA and Jest, but here is a list of bugs related to Jest being slightly misaligned with the regular Node runtime:

• Missing node global performance in test environment jestjs/jest#11629
• ArrayBuffer regression in node env jestjs/jest#7780
• Jest globals differ from Node globals jestjs/jest#2549

The latter contains the core of the issue really.

To summarize:

• The main motivation to move from Jest to AVA would be to run in a "vanilla" Node runtime to avoid missing or hitting such issues.
• As far as end-to-end tests are concerned, AVA and Jest have all the required features, so there's no reason to use one over the other at this level.
• The tests are as readable using one framework or the other
• Our unit tests are written in Jest and would remain so in the foreseeable future, so moving the end-to-end tests to AVA introduces a new dependency and a different test framework, which is not a big deal but a (small) price to pay still.

[matthieubosquet]

The issue with Jest globals seems pretty bad but I'm not sure how much it affects us.

I would tend to lean towards keeping the number of dependencies to a minimum and migrate if and when we hit a serious bottleneck with Jest (I'm not best placed to determine whether we have or not).

[NSeydoux]

Migrating the end-to-end tests to AVA should work, but it is low-priority. Closing this for now, but keeping it around.