diff --git a/testsuite/datmantests/test_mysql_helper.py b/testsuite/datmantests/test_mysql_helper.py
index 5f6d1ea..3fa9fee 100644
--- a/testsuite/datmantests/test_mysql_helper.py
+++ b/testsuite/datmantests/test_mysql_helper.py
@@ -51,7 +51,7 @@ class TestPostgresHelper(TestCase):
         self.assertEqual(proc.wait(), 0)
         self.assertIn(b"CREATE TABLE", stdout)
         self.assertIn(b"INSERT INTO", stdout)
-        print(stdout) # TODO
+        print(stdout)  # TODO
 
     def test_backup_and_extraction(self):
         td = TemporaryDirectory("test_my_bae")
diff --git a/testsuite/helpers/yama_helpers.py b/testsuite/helpers/yama_helpers.py
index 9954ea7..895194f 100644
--- a/testsuite/helpers/yama_helpers.py
+++ b/testsuite/helpers/yama_helpers.py
@@ -6,5 +6,7 @@ from pathlib import Path
 def set_up_simple_yama(path: Path):
     path.mkdir(exist_ok=True)
     subprocess.check_call(("yama", "init"), cwd=path)
-    example_zstd_path = Path(__file__).parent.parent.parent.joinpath("example_zstd.dict")
+    example_zstd_path = Path(__file__).parent.parent.parent.joinpath(
+        "example_zstd.dict"
+    )
     shutil.copyfile(example_zstd_path, path.joinpath("important_zstd.dict"))
diff --git a/testsuite/yamatests/test_check_and_gc.py b/testsuite/yamatests/test_check_and_gc.py
index 25f4324..68d49e0 100644
--- a/testsuite/yamatests/test_check_and_gc.py
+++ b/testsuite/yamatests/test_check_and_gc.py
@@ -1,10 +1,12 @@
+import re
 import subprocess
 from pathlib import Path
 from random import Random
 from tempfile import TemporaryDirectory
+from typing import Optional
 from unittest import TestCase
 
-from helpers import generate_random_dir
+from helpers import generate_random_dir, randomly_mutate_directory_in_descriptor
 from helpers.datman_helpers import set_up_simple_datman
 from helpers.yama_helpers import set_up_simple_yama
 
@@ -15,7 +17,6 @@ class TestYamaCheck(TestCase):
         tdpath = Path(td.name)
 
         datman_path = tdpath.joinpath("datman")
-        _src_path = datman_path.joinpath("srca")
         yama_path = datman_path.joinpath("main")
 
         set_up_simple_datman(datman_path)
@@ -23,9 +24,17 @@ class TestYamaCheck(TestCase):
 
         subprocess.check_call(("yama", "check", "--shallow"), cwd=yama_path)
         subprocess.check_call(("yama", "check", "--deep"), cwd=yama_path)
-        output = subprocess.check_output(("yama", "check", "--shallow", "--apply-gc"), cwd=yama_path, stderr=subprocess.STDOUT)
+        output = subprocess.check_output(
+            ("yama", "check", "--shallow", "--apply-gc"),
+            cwd=yama_path,
+            stderr=subprocess.STDOUT,
+        )
         self.assertIn(b" 0 chunks", output)
-        output = subprocess.check_output(("yama", "check", "--deep", "--apply-gc"), cwd=yama_path, stderr=subprocess.STDOUT)
+        output = subprocess.check_output(
+            ("yama", "check", "--deep", "--apply-gc"),
+            cwd=yama_path,
+            stderr=subprocess.STDOUT,
+        )
         self.assertIn(b" 0 chunks", output)
         td.cleanup()
 
@@ -50,11 +59,25 @@ class TestYamaCheck(TestCase):
 
         subprocess.check_call(("yama", "check", "--shallow"), cwd=yama_path)
         subprocess.check_call(("yama", "check", "--deep"), cwd=yama_path)
-        output = subprocess.check_output(("yama", "check", "--shallow", "--apply-gc"), cwd=yama_path,
-                                         stderr=subprocess.STDOUT)
+
+        ec_shallow = subprocess.Popen(
+            ("yama", "check", "--shallow"), cwd=yama_path
+        ).wait()
+        self.assertEqual(ec_shallow, 0)
+        ec_deep = subprocess.Popen(("yama", "check", "--deep"), cwd=yama_path).wait()
+        self.assertEqual(ec_deep, 0)
+
+        output = subprocess.check_output(
+            ("yama", "check", "--shallow", "--apply-gc"),
+            cwd=yama_path,
+            stderr=subprocess.STDOUT,
+        )
         self.assertIn(b" 0 chunks", output)
-        output = subprocess.check_output(("yama", "check", "--deep", "--apply-gc"), cwd=yama_path,
-                                         stderr=subprocess.STDOUT)
+        output = subprocess.check_output(
+            ("yama", "check", "--deep", "--apply-gc"),
+            cwd=yama_path,
+            stderr=subprocess.STDOUT,
+        )
         self.assertIn(b" 0 chunks", output)
         td.cleanup()
 
@@ -88,9 +111,14 @@ class TestYamaCheck(TestCase):
                 fvictim.write(b"\x01")
             else:
                 fvictim.write(b"\0")
-            print(f"Corrupted byte {byte_to_eat} of {size_in_bytes}. Was {existing_byte!r}.")
+            print(
+                f"Corrupted byte {byte_to_eat} of {size_in_bytes}."
+                f" Was {existing_byte!r}."
+            )
 
-        ec_shallow = subprocess.Popen(("yama", "check", "--shallow"), cwd=yama_path).wait()
+        ec_shallow = subprocess.Popen(
+            ("yama", "check", "--shallow"), cwd=yama_path
+        ).wait()
         ec_deep = subprocess.Popen(("yama", "check", "--deep"), cwd=yama_path).wait()
 
         # shallow checks won't always raise the issue