Experimental test interface

[novemberborn]

This kicks off some experimental changes to AVA's test interface. That is, the const test = require('ava') stuff. Eventually this will be come AVA 4, but initially it'll be available through importing ava/experimental. You'll also have to enable the experimentalTestInterfaces experiment.

Summary of (planned) changes:

• AVA is now just a CJS module with a single export: the test function. If you're transpiling ESM, you'll no longer be able to import { serial } from 'ava'. This never worked anyway with proper ESM.
• Test implementations can no longer have title functions.
• You'll no longer be able to pass an array of macros (or implementations), when declaring tests or with t.try().
• Speaking of macros, if you want them to have a title function you'll need to use test.macro({ exec (t) { … }, title () { return 'title' }).
• If you're writing tests using TypeScript, the Macro type has changed.
• But, on the plus side, test.macro() automatically uses the t.context type from test.

I tend to write service integration tests using AVA, which involve stubbing several APIs, managing database access and launching child processes. Crafting t.context for these tests is rather complicated.

I'm tinkering with a "forkable test interface". You'd start off calling test.make(). This gives you an entirely new test chain, say test2. You can define hooks and whatnot, and then call test2.fork() to create yet another test chain, which will use the hooks defined on test2 before forking.

You'll be able to pass some options to make() and fork() to construct t.context, along the lines of what you'd do using test.before() and test.beforeEach(). But, for TypeScript users, the context type will be inferable.

We could also use this to create a test chain that always executes serially, or limits concurrency, or runs in isolation from other test chains in the same test file, or executes conditionally.

More to come!

[papb]

But, for TypeScript users, the context type will be inferable.

Hi @novemberborn, currently to get accurate type checking for t.context, I do the following:

import test, { TestInterface } from 'ava';

function wrapTest(test: TestInterface): asserts test is TestInterface<MyContextType> {
	test.beforeEach(t => {
		t.context = getMyContext();
	});
}

wrapTest(test);

test('foo', /* ... */);

And it works very well. Just in case it can help you have some ideas :)

[novemberborn]

@papb that's a nice trick! Would you like to add it to our TypeScript recipe?

[papb]

Hi @novemberborn, sorry for taking long to reply, I would but I don't have the time, if you like it please feel free to add it, no need to credit or anything :)

[novemberborn]

I've added this to the AVA 4 milestone… I don't expect to land everything but would like to get at least the breaking changes in.

[novemberborn]

Other than the "forkable" stuff, this is now in #2785 instead.