Remove defaults for private code

[novemberborn]

AVA exposes two public interfaces: the CLI and the programmatic API. All other code is private. Currently a lot of the private code has defaults, e.g. Runner can be instantiated without options.

This tends to happen in tests and causes confusion where code has to be extra defensive against scenarios that wouldn't occur if defaults were set at the public interface level.

Allowing defaults throughout the code makes it hard to reason about expected values. I'm proposing we remove defaults from internal code and make our tests more explicit.

Thoughts?

[vadimdemedes]

I think we shouldn't do it, because those libraries/components should be stable on their own. They should not depend on other code passing these arguments correctly.

Allowing defaults throughout the code makes it hard to reason about expected values.

We can improve our checking of value types, using functions like Array.isArray(), so that it's more clear what we're expecting.

[novemberborn]

I think we shouldn't do it, because those libraries/components should be stable on their own

Sure, they'd just require valid options to be passed.

[novemberborn]

@avajs/core any thoughts on this?

[sindresorhus]

👍 Sounds good.

[novemberborn]

We'll just do this when we're touching code. No need to keep the issue open.