New snapshot tests (#134)

* Changes project-related structures to use `BTreeMap` instead of `HashMap` for children to aid determiniusm
* Changes imfs-related structures to have total ordering and use `BTreeSet` instead of `HashSet`
* Upgrades dependencies to `bx_dom_weak`1.2.0 and rbx_xml 0.5.0 to aid in more determinism stuff
* Re-exposes the `RbxSession`'s root project via `root_project()`
* Implements `Default` for a couple things
* Tweaks visualization code to support visualizing trees not attached to an `RbxSession`
* Adds an ID-invariant comparison method for `rbx_tree` relying on previous determinism changes
* Adds a (disabled) test to start finding issues in the reconciler with regards to communicativity of snapshot application
* Adds a snapshot testing system that operates on `RbxTree` and associated metadata, which are committed in this change

server/tests/tree_snapshots.rs

@@ -0,0 +1,68 @@
+mod test_util;
+
+use std::{
+    fs,
+    path::{Path, PathBuf},
+    sync::Arc,
+    thread,
+    time::Duration,
+};
+
+use tempfile::{tempdir, TempDir};
+
+use librojo::{
+    live_session::LiveSession,
+    project::Project,
+};
+
+use crate::test_util::{
+    copy_recursive,
+    tree::tree_step,
+};
+
+#[test]
+fn multi_partition_game() {
+    let _ = env_logger::try_init();
+    let source_path = project_path("multi_partition_game");
+
+    let (dir, live_session) = start_session(&source_path);
+    tree_step("initial", &live_session, &source_path);
+
+    let added_path = dir.path().join("a/added");
+    fs::create_dir_all(&added_path)
+        .expect("Couldn't create directory");
+    thread::sleep(Duration::from_millis(250));
+
+    tree_step("with_dir", &live_session, &source_path);
+
+    let moved_path = dir.path().join("b/added");
+    fs::rename(&added_path, &moved_path)
+        .expect("Couldn't rename directory");
+    thread::sleep(Duration::from_millis(250));
+
+    tree_step("with_moved_dir", &live_session, &source_path);
+}
+
+/// Find the path to the given test project relative to the manifest.
+fn project_path(name: &str) -> PathBuf {
+    let mut path = Path::new(env!("CARGO_MANIFEST_DIR")).join("../test-projects");
+    path.push(name);
+    path
+}
+
+/// Starts a new LiveSession for the project located at the given file path.
+fn start_session(source_path: &Path) -> (TempDir, LiveSession) {
+    let dir = tempdir()
+        .expect("Couldn't create temporary directory");
+
+    copy_recursive(&source_path, dir.path())
+        .expect("Couldn't copy project to temporary directory");
+
+    let project = Arc::new(Project::load_fuzzy(dir.path())
+        .expect("Couldn't load project from temp directory"));
+
+    let live_session = LiveSession::new(Arc::clone(&project))
+        .expect("Couldn't start live session");
+
+    (dir, live_session)
+}