Ensure ExecutionContext properties are not enumerable
Ensure ExecutionContext properties are not enumerable

There's no point in revealing the internal Test object when users try to
log the `t` object.

Collinslenjo/ava,avajs/ava,Collinslenjo/ava,avajs/ava,andywer/ava-ts,andywer/ava-ts,sindresorhus/ava