diff --git a/testsuite/helpers/__init__.py b/testsuite/helpers/__init__.py
index cf75c23..d9789d5 100644
--- a/testsuite/helpers/__init__.py
+++ b/testsuite/helpers/__init__.py
@@ -188,12 +188,26 @@ def randomly_mutate_file_in_descriptor(
 
 
 def randomly_mutate_directory_in_descriptor(
-    descriptor: DirectoryDescriptor, path: Path, random: Random
+    descriptor: DirectoryDescriptor, path: Path, rng: Random
 ) -> None:
     for name, value in descriptor.contents.items():
-        if isinstance(value, FileDescriptor):
-            if random.random() < 0.6:
-                randomly_mutate_file_in_descriptor(value, path.joinpath(name), random)
+        if rng.random() < 0.1:
+            # just delete this (with low 10% chance)
+            continue
+        elif isinstance(value, FileDescriptor):
+            if rng.random() < 0.6:
+                randomly_mutate_file_in_descriptor(value, path.joinpath(name), rng)
         else:
             assert isinstance(value, DirectoryDescriptor)
-            randomly_mutate_directory_in_descriptor(value, path.joinpath(name), random)
+            randomly_mutate_directory_in_descriptor(value, path.joinpath(name), rng)
+
+    # introduce some new files, maybe.
+    new_files_to_introduce = max(0, rng.randint(-3, 3))
+    for _ in range(new_files_to_introduce):
+        filename_len = rng.randint(4, 16)
+        filename = "".join(rng.choice(ALPHABET) for _ in range(filename_len))
+        filepath = path.joinpath(filename)
+        if rng.random() < 0.8:
+            generate_random_file(rng, filepath)
+        else:
+            generate_random_dir(rng, filepath, 5)