sub test_someting($tempdir) {
    ...
}
[download]

If you look at the modules in the t/ directory, those are all examples on how to use the module to write tests.

Is there a reason why they need to be available as parameters at all? These fixtures could just be global variables, couldn't they?

They could, but this way they are localized to the function, they go out of scope after the function is done and one test will not impact another test.

I may have trouble understanding the full intention.... please help me:

You want to parse

sub test_someting($tempdir) {
    # do some tests
}
[download]

And because you see the (registered) keyword "tempdir" your test system is supposed to call this test with a prepared temporary directory?

ok(
    test_something( create_tempdir() ),
    "something",
)
[download]

Kind of a naming convention?

Did I get it right?

If yes, I could think of some alternative (and more perlish) ways to achieve this without needing to parse the signature.

PS: not sure why you call this "dependency injection" or do you plan testruns where the injected $tempdir is not a temporary dir? :)

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery}

Yes. "dependency injection" is how this is called in the case of pytest, maybe it is not a generic term. You could create your own "fixture" and then you or others could set its name as a parameter.

I put together an example of creating and registering a fixture and then also use that fixture.

I would love to see your suggestion for more Perlish way.