Add deterministic test & extract time formatter for list_files (#616)

[octoaide]

Closes #616

Summary

Prepare tests for the upcoming chrono -> jiff migration by isolating the time formatting logic and adding a deterministic test for list_files modified-time output.

What I changed

• Extracted a helper format_modified_time(SystemTime) -> String in src/root/ifconfig.rs to centralize the local-time formatting (currently using chrono with format "%Y/%m/%d %T"). This makes it easy to replace the implementation later with jiff without modifying list_files logic.
• Updated list_files to call the new helper, simplifying the loop body.
• Added test list_files_formats_modified_time_in_local_timezone that:
  • Sets TZ=UTC (using the existing pattern with unsafe std::env::set_var) so local-time formatting is deterministic in CI and locally.
  • Uses hard-coded expected strings for fixed timestamps (UNIX_EPOCH and UNIX_EPOCH + 1_700_000_000s) instead of computing expected values with a time crate.
  • Does not introduce chrono or jiff just for test expectations.

Notes and verification

• Only src/root/ifconfig.rs was modified.
• Cargo.toml is unchanged.
• Tests were run locally: cargo test list_files (and full test & clippy runs). All relevant tests pass.

Why

This change prepares the codebase for a safe swap from chrono to jiff by:

• Isolating the formatting logic into a single function so the swap is localized to one place.
• Adding a deterministic test that asserts the exact local-time formatted output (YYYY/MM/DD HH:MM:SS) using fixed expected strings, preventing regressions.

Closes #616.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.90%. Comparing base (f462850) to head (9b8366e).

Files with missing lines	Patch %	Lines
src/root/ifconfig.rs	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #619      +/-   ##
==========================================
- Coverage   80.99%   80.90%   -0.09%     
==========================================
  Files          27       27              
  Lines        3977     3954      -23     
==========================================
- Hits         3221     3199      -22     
+ Misses        756      755       -1     

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[zmrdltl]

Please revert the production refactor and keep this PR focused on adding the deterministic list_files modified-time output test.

For example:

const LIST_FILES_MTIME_CHILD_ENV: &str = "ROXY_LIST_FILES_MTIME_CHILD";
...
#[test]
fn list_files_formats_modified_time_in_local_timezone() {
    if std::env::var_os(LIST_FILES_MTIME_CHILD_ENV).is_some() {
        let dir = make_temp_test_dir("list-mtime");
        let file_path = dir.join("fixed.yaml");
        write_text_file(&file_path, "fixed");

        let ts = UNIX_EPOCH + Duration::from_secs(1_700_000_000);
        let file = OpenOptions::new()
            .write(true)
            .open(&file_path)
            .expect("test file should be openable for timestamp update");
        file.set_modified(ts)
            .expect("test file modified time should be settable");

        let listed = list_files(
            dir.to_str().expect("temp path should be valid utf-8"),
            None,
            false,
        )
        .expect("listing files should succeed");
        assert_eq!(
            listed,
            vec![(
                5,
                "2023/11/14 22:13:20".to_string(),
                "fixed.yaml".to_string()
            )]
        );

        fs::remove_dir_all(&dir).expect("temp test directory should be removable");
        return;
    }

    let output = std::process::Command::new(
        std::env::current_exe().expect("current test executable should be available"),
    )
    .arg("list_files_formats_modified_time_in_local_timezone")
    .env(LIST_FILES_MTIME_CHILD_ENV, "1")
    .env("TZ", "UTC")
    .output()
    .expect("child test process should run");

    assert!(
        output.status.success(),
        "child test process should pass\nstdout:\n{}\nstderr:\n{}",
        String::from_utf8_lossy(&output.stdout),
        String::from_utf8_lossy(&output.stderr)
    );
}

[octoaide]

Thanks — I reviewed your comment and updated the PR accordingly.

I reverted the production refactor and restored the original inline DateTime formatting in list_files (removed the format_modified_time helper and dropped the time::SystemTime import). I also replaced the test with the child-process pattern you suggested: the parent re-execs the test binary with TZ=UTC and ROXY_LIST_FILES_MTIME_CHILD=1, and the child branch creates a temp file, sets its mtime to 1_700_000_000, and asserts that list_files returns the expected tuple (5, "2023/11/14 22:13:20", "fixed.yaml").

I've committed and pushed these changes. I ran the tests and cargo clippy — all three list_files tests pass and clippy is clean.

Thanks for the guidance — this PR is now focused on the deterministic modified-time test as requested.

[sae-bom]

@zmrdltl Please update the direction of this issue based on the comments on the parent issue.

[zmrdltl]

@sae-bom I updated #616 to match the direction from the parent issue discussion. Once this work is completed, the other sibling issues will no longer be needed, so I’ll close them as superseded.

[zmrdltl]

@octoaide Please update the work to match the revised direction in #616.

[octoaide]

I reviewed the direction from #616 and pivoted the PR to match it (per @zmrdltl). Instead of preparing a chrono→jiff swap, I removed direct chrono usage entirely and simplified the API where chrono had been needed.

What I changed (all committed and pushed):

• list_files now returns Vec (just file names). Callers never used size or modified-time, so keeping only names simplifies things.
• load_netplan_yaml and NetplanYaml::apply were updated to consume the simpler return type.
• Removed the format_modified_time helper and the related test (they're no longer applicable).
• Removed chrono from Cargo.toml.
• Added an Unreleased entry to CHANGELOG.

Verification:

• cargo build, cargo test, and cargo clippy --all-targets -- -D warnings all pass.
• No direct chrono usage remains in Cargo.toml, src/, or tests/.

Thanks for the guidance — I’ve updated the work to follow the revised direction and confirmed everything is addressed.