diff --git a/test/run/test_assemblers.py b/test/run/test_assemblers.py
index 2b46cc2d..089e90a2 100644
--- a/test/run/test_assemblers.py
+++ b/test/run/test_assemblers.py
@@ -25,7 +25,7 @@ class TestAssemblers(test.TestBase):
         super().setUpClass()
 
     def setUp(self):
-        self.osbuild = test.OSBuild(self)
+        self.osbuild = test.OSBuild()
 
     @contextlib.contextmanager
     def run_assembler(self, osb, name, options, output_path):
@@ -223,7 +223,7 @@ class TestAssemblers(test.TestBase):
                                         options,
                                         filename) as (tree, image):
                     output = subprocess.check_output(["file", "--mime-type", image], encoding="utf-8")
-                    _, mimetype = output.strip().split(": ") # "filename: mimetype"
+                    _, mimetype = output.strip().split(": ")  # "filename: mimetype"
                     self.assertIn(mimetype, expected_mimetypes)
 
                     if compression:
@@ -245,6 +245,7 @@ class TestAssemblers(test.TestBase):
                         self.assertEqual(diff["deleted_files"], [])
                         self.assertEqual(diff["differences"], {})
 
+
 @contextlib.contextmanager
 def loop_create_device(ctl, fd, offset=None, sizelimit=None):
     while True:
diff --git a/test/run/test_boot.py b/test/run/test_boot.py
index 8e8ffbaa..c66e1303 100644
--- a/test/run/test_boot.py
+++ b/test/run/test_boot.py
@@ -14,7 +14,7 @@ from .. import test
 @unittest.skipUnless(test.TestBase.can_bind_mount(), "root-only")
 class TestBoot(test.TestBase):
     def setUp(self):
-        self.osbuild = test.OSBuild(self)
+        self.osbuild = test.OSBuild()
 
     def test_boot(self):
         #
diff --git a/test/run/test_executable.py b/test/run/test_executable.py
index 72a3c1a7..3956e47b 100644
--- a/test/run/test_executable.py
+++ b/test/run/test_executable.py
@@ -11,7 +11,7 @@ from .. import test
 
 class TestExecutable(unittest.TestCase):
     def setUp(self):
-        self.osbuild = test.OSBuild(self)
+        self.osbuild = test.OSBuild()
 
     def test_invalid_manifest(self):
         invalid = json.dumps({"foo": 42})
diff --git a/test/run/test_noop.py b/test/run/test_noop.py
index efd5c44c..c82883f3 100644
--- a/test/run/test_noop.py
+++ b/test/run/test_noop.py
@@ -33,9 +33,10 @@ NOOP_V2 = {
     ]
 }
 
+
 class TestNoop(unittest.TestCase):
     def setUp(self):
-        self.osbuild = test.OSBuild(self)
+        self.osbuild = test.OSBuild()
 
     def test_noop(self):
         #
@@ -55,7 +56,6 @@ class TestNoop(unittest.TestCase):
             osb.compile("{}")
             osb.compile("{}")
 
-
     def test_noop_v2(self):
         with tempfile.TemporaryDirectory() as tmp:
             with self.osbuild as osb:
diff --git a/test/run/test_stages.py b/test/run/test_stages.py
index 7d5a8948..00139670 100644
--- a/test/run/test_stages.py
+++ b/test/run/test_stages.py
@@ -150,7 +150,7 @@ class TestStages(test.TestBase):
             shutil.rmtree(cls.store)
 
     def setUp(self):
-        self.osbuild = test.OSBuild(self, cache_from=self.store)
+        self.osbuild = test.OSBuild(cache_from=self.store)
 
     def run_stage_diff_test(self, test_dir: str):
         with self.osbuild as osb:
diff --git a/test/test.py b/test/test.py
index 22786679..2bc15793 100644
--- a/test/test.py
+++ b/test/test.py
@@ -217,14 +217,12 @@ class OSBuild(contextlib.AbstractContextManager):
     when exiting.
     """
 
-    _unittest = None
     _cache_from = None
 
     _exitstack = None
     _cachedir = None
 
-    def __init__(self, unit_test, cache_from=None):
-        self._unittest = unit_test
+    def __init__(self, *, cache_from=None):
         self._cache_from = cache_from
 
     def __enter__(self):
@@ -331,7 +329,7 @@ class OSBuild(contextlib.AbstractContextManager):
             if check:
                 raise subprocess.CalledProcessError(p.returncode, cmd_args, data_stdout, data_stderr)
             self._print_result(p.returncode, data_stdout, data_stderr)
-            self._unittest.assertEqual(p.returncode, 0)
+            assert p.returncode == 0
 
         return json.loads(data_stdout)