tests/Integration: Add FileTest

[jtojnar]

This is a regression test for #812.

[jtojnar]

@Art4 Do you think something like this is reasonable?

I tried finding a library for the PHP server but after reviewing the following, I gave up and wrote my own helper class:

• https://packagist.org/packages/internations/http-mock
  • no PHP 8 support
  • incompatible dependencies
  • no open port selection
  • unmaintained
• https://packagist.org/packages/pagely/http-mock
  • fork of the above
  • no open port selection
  • still incompatible dependencies
  • unmaintained
• https://packagist.org/packages/elnoro/php-http-mock
  • 👍 minimal codebase
  • requires PHP 8
  • no open port selection
  • no released versions
• https://github.com/LibreSign/behat-builtin-extension
  • 👍 minimal codebase
  • 👍 open port selection
  • undeclared behat dependency
  • AGPL licensed
• https://packagist.org/packages/mcustiel/phiremock-server
  • complex configuration
• https://packagist.org/packages/ciareis/bypass
  • old version still supports PHP 7.2
    • but port autodetection only works on PHP 8 (using php -S localhost: flag)

[Art4]

I would have said that it is not worth the effort to create such a test because the File class will be deprecated. But since you've already done the work, we can keep the test. Requiring a separate library for it would definitely be too much.

[jtojnar]

Thanks for the review, updated. I think this integration test will be useful for PSR-18 as well since how the permanent/temporary redirection interact with get_final_url is non-trivial. Though there we at least will not need to spawn a server since that will support mocking.