test: Improve ExplicitIndirectVariableFixerTest

[Wirone]

• add more test cases
• add yield keys (better --testdox output)
• add missing iterable type for PHPStan

Related to #7442.

[coveralls]

coverage: 94.795%. remained the same
when pulling 1f3e726 on Wirone:codito/improve-explicit_indirect_variable-test-cases
into f34d12c on PHP-CS-Fixer:master.

[keradus]

Suggested change

	* @return iterable<string, array{0: string, 1?: null|string}>
	* @return iterable<string, array{0: string, 1?: string}>

[Wirone]

Technically it's possible to return null explicitly as a second array item and it will work, because testFix signature allows it. I just reflected the actual contract 🙂.

[keradus]

it's technically possible to provide null to testFix, but I wouldn't like to have provider explicitly returning null.

IMHO we shall have same approaches for all providers, i was always using 1?: string. if you want to change approach, please change for whole project.

but again, i would avoid provider returning null, either 0: string, 1?: string or 0: string, 1: null|string. combining ? with |null is overkill and bringing more than one way to provide data cases

[Wirone]

I agree, but it's forward-compatible with providers returning more than 2 elements, e.g. rules configuration. I am pretty sure there are already places where input is explicitly returned as null because of that.

[Wirone]

@keradus the example: signature + test case with explicit null as the input value. I know it can be changed later if third argument is introduced, but I think it's good to describe existing contract from the beginning.

[kubawerlos]

LGTM, the discussion about the PHPDoc is not really related to the topic of this PR, I believe we can shift such discussion to separate conversations.