feat: module of utilities for integration tests

[JyJyJcr]

Proposed changes

This PR adds test_util module, utilities for integration tests of Nginx modules. The utilities were moved from tests/log_test.rs, and fixed to use the bundled Nginx used in bindings, the install path of which is recorded in nginx-sys::metadata::NGINX_INSTALL_DIR.

Checklist

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[dekobon]

Hi there, once again thank you for all of your contributions. I talked over this PR with some of the other project maintainers and there is a strong opinion that this functionality may be better in another project/library that supplements ngx-rust. Would it be possible to do that rather than integrate it into the core SDK?

[JyJyJcr]

Of course possible (and I agree to split it from the core), but before changing let me clarify which is better, creating a new GitHub repository, or just separating it into a new subdirectory in this repository, just like nginx-sys?
Sidenote: we need to keep nginx-sys::metadata module to salvage build informations for integration tests in either case.

[bavshin-f5]

Sidenote: we need to keep nginx-sys::metadata module to salvage build informations for integration tests in either case.

There's nginx-sys::NGX_PREFIX that already contains the installation path (NULL-terminated u8 slice, so you need to strip the last byte and use std::os::unix::ffi::OsStrExt).

It's also optional and could be omitted by the buildsystem if you specify an empty --prefix (we do that for the official Windows builds), but that's only a problem with non-vendored Nginx source tree.

[JyJyJcr]

There's nginx-sys::NGX_PREFIX that already contains the installation path (NULL-terminated u8 slice, so you need to strip the last byte and use std::os::unix::ffi::OsStrExt).

Thank you for important information. Now test_util directly uses constants in bindings.rs (not only NGX_PREFIX but also other configurations, such as NGX_CONF_PATH).