Add test harness

[9999years]

The GhcidNg type copies a given directory to a tempdir and then launches ghcid-ng there. It also spawns an async task to read JSON log events from the log file.

GhcidNg uses thread-local storage to determine which version of ghc to use when launching tests, and will error appropriately if the thread-local storage is not set. This takes advantage of the fact that async tests run in the tokio "current-thread" runtime by default, which schedules all tasks in the test on the same thread.

The second part is a proc macro attribute exported as #[test_harness::test], which rewrites tests so that

1. The tests are async functions which run under the default #[tokio::test] current-thread runtime.
2. Tracing is set up in the tests so that log messages from the test-harness library are visible in the test output.
3. The appropriate thread-local variables are set for each test (this includes the current GHC version).
4. One test is generated for each GHC version.
5. If tests fail, the relevant ghcid-ng logs are saved to a directory under target/ and the path is printed at the end of the tests.

Here's a sample test from #44 using this test harness:

/// Test that `ghcid-ng` can start up and then reload on changes.
#[test]
async fn can_reload() {
    let mut session = GhcidNg::new("tests/data/simple")
        .await
        .expect("ghcid-ng starts");
    session
        .wait_until_ready()
        .await
        .expect("ghcid-ng loads ghci");
    fs::append(session.path("src/MyLib.hs"), "\n\nhello = 1\n")
        .await
        .unwrap();
    session
        .wait_until_reload()
        .await
        .expect("ghcid-ng reloads on changes");
    session
        .get_log(
            Matcher::span_close()
                .in_module("ghcid_ng::ghci")
                .in_spans(["on_action", "reload"]),
        )
        .await
        .expect("ghcid-ng finishes reloading");
}

[linear]

DUX-1327 Add test harness

Add the proc-macro-based test harness itself.

[9999years]

Current dependencies on/for this PR:

• main
  • PR Use crane for Nix builds #54
    • PR Move to multi-crate workspace #55
      • PR Add test Haskell project #56
        • PR Add IO helpers for test harness #61
          • PR Add tracing JSON reader to test-harness #62
            • PR Add tracing event matcher to test-harness #63
              • PR Add test harness #57 👈
                • PR Add integration tests #44

This comment was auto-generated by Graphite.

[Gabriella439]

Have you had to make use of this fallback code path for removing the directory? In other words, has rm -rf succeeded where remove_dir_all failed?