I guess Linux doesn't iterate over folders alphabetically.

pkg/watcher/test/directory_watcher/shared.dart

Index: pkg/watcher/test/directory_watcher/shared.dart
diff --git a/pkg/watcher/test/directory_watcher/shared.dart b/pkg/watcher/test/directory_watcher/shared.dart
index f831196a89533c6cfbfca85064b6c27d4df23b5c..2e0186f5206b52c7b9c9173a0bce0b75e0ed194d 100644
--- a/pkg/watcher/test/directory_watcher/shared.dart
+++ b/pkg/watcher/test/directory_watcher/shared.dart
@@ -55,10 +55,13 @@ sharedTests() {
     writeFile("a.txt", contents: "same");
     writeFile("b.txt", contents: "before");
     startWatcher();
+
     writeFile("a.txt", contents: "same");
     writeFile("b.txt", contents: "after");
-    expectModifyEvent("a.txt");
-    expectModifyEvent("b.txt");
+    inAnyOrder(() {
+      expectModifyEvent("a.txt");
+      expectModifyEvent("b.txt");
+    });
   });
 
   test('when the watched directory is deleted, removes all files', () {