Enable to type t.context by extending module interface

[acro5piano]

Thank you for the great tool.

Summary

This Pull Request introduces a new AvaContext interface that can be augmented by library users. By allowing developers to declare custom fields in their test context, this change provides greater flexibility and type safety when writing tests in TypeScript.

Details of Changes

• Added AvaContext Interface
  • Introduced a new AvaContext interface
  • Updated TestFn to default its generic Context to AvaContext
• Updated corresponding docs

Library users can now directly extend the AvaContext interface to add custom properties in tests, which could be impressive when using shared context:

declare module 'ava' {
  interface AvaContext {
    foo: string;
  }
}

Difference between TestFn

There is already a guide to type t.context:

const test = anyTest as TestFn<{foo: string}>;

This PR provides another method to type the context without creating a new variable, which make users ease to use context values.

[novemberborn]

@sindresorhus what are your thoughts on using extensible interfaces like this?

[novemberborn]

I've noticed that XO now recommends using types, not interfaces. I also don't like how this would apply across your project, yet it's not unusual to have different contexts in different files.

Closing for now, perhaps this is better as a Discussion first.

[acro5piano]

@novemberborn Thank you for your review!

I've noticed that XO now recommends using types, not interfaces.

Yes, I saw the lint errors. Note that this feature cannot be implemented by type, because type is not extendable while interface can be extended.

I also don't like how this would apply across your project, yet it's not unusual to have different contexts in different files.

That's a fair reason to reject this PR, still users can choose explicit typing the context if they want.

Closing for now, perhaps this is better as a Discussion first.

Agree! Thanks for considering it.