avoid racyness in worktree tests (#301)

Author: Byron

git-worktree/tests/worktree/index/checkout.rs

@@ -287,21 +287,27 @@ fn keep_going_collects_results() {
     )
     .unwrap();
 
-    assert_eq!(
-        sort_when_threaded(
+    if multi_threaded() {
+        assert_eq!(
+            outcome.errors.len(),
+            2,
+            "content changes due to non-deterministic nature of racy threads"
+        )
+    } else {
+        assert_eq!(
             outcome
                 .errors
                 .iter()
                 .map(|r| r.path.to_path_lossy().into_owned())
-                .collect()
-        ),
-        sort_when_threaded(paths(if cfg!(unix) {
-            ["dir/content", "empty"]
-        } else {
-            // not actually a symlink anymore, even though symlinks are supported but git think differently.
-            ["dir/content", "dir/sub-dir/symlink"]
-        }))
-    );
+                .collect::<Vec<_>>(),
+            paths(if cfg!(unix) {
+                ["dir/content", "empty"]
+            } else {
+                // not actually a symlink anymore, even though symlinks are supported but git think differently.
+                ["dir/content", "dir/sub-dir/symlink"]
+            })
+        );
+    }
 
     assert_eq!(
         stripped_prefix(&destination, &dir_structure(&destination)),
@@ -349,8 +355,7 @@ fn collisions_are_detected_on_a_case_insensitive_filesystem() {
     );
 
     let dest_files = dir_structure(&destination);
-    let multi_threaded = git_features::parallel::num_threads(None) > 1;
-    if multi_threaded {
+    if multi_threaded() {
         assert_eq!(
             dest_files.len(),
             5,
@@ -370,7 +375,7 @@ fn collisions_are_detected_on_a_case_insensitive_filesystem() {
     #[cfg(not(windows))]
     let error_kind_dir = error_kind;
 
-    if multi_threaded {
+    if multi_threaded() {
         assert_eq!(
             outcome.collisions.len(),
             5,
@@ -406,6 +411,10 @@ fn collisions_are_detected_on_a_case_insensitive_filesystem() {
     }
 }
 
+fn multi_threaded() -> bool {
+    git_features::parallel::num_threads(None) > 1
+}
+
 fn assert_equality(source_tree: &Path, destination: &TempDir, allow_symlinks: bool) -> crate::Result<usize> {
     let source_files = dir_structure(source_tree);
     let worktree_files = dir_structure(&destination);
@@ -517,13 +526,3 @@ fn opts_from_probe() -> index::checkout::Options {
 fn paths<'a>(p: impl IntoIterator<Item = &'a str>) -> Vec<PathBuf> {
     p.into_iter().map(PathBuf::from).collect()
 }
-
-fn sort_when_threaded<T>(mut p: Vec<T>) -> Vec<T>
-where
-    T: Ord,
-{
-    if git_features::parallel::num_threads(None) > 1 {
-        p.sort()
-    }
-    p
-}