diff --git a/stix2/test/test_properties.py b/stix2/test/test_properties.py
index 60a42e6..ea9a003 100644
--- a/stix2/test/test_properties.py
+++ b/stix2/test/test_properties.py
@@ -3,10 +3,9 @@ import datetime as dt
 import pytest
 import pytz
 
-import stix2
 from stix2.base import _STIXBase
 from stix2.exceptions import (
-    ExtraPropertiesError, STIXError, CustomContentError,
+    CustomContentError, ExtraPropertiesError, STIXError,
 )
 from stix2.properties import (
     BinaryProperty, BooleanProperty, EmbeddedObjectProperty, EnumProperty,
diff --git a/stix2/test/v20/test_properties.py b/stix2/test/v20/test_properties.py
index 4dbc437..0158f9a 100644
--- a/stix2/test/v20/test_properties.py
+++ b/stix2/test/v20/test_properties.py
@@ -9,14 +9,13 @@ from stix2.exceptions import (
 )
 from stix2.properties import (
     DictionaryProperty, EmbeddedObjectProperty, ExtensionsProperty,
-    HashesProperty, ListProperty, ObservableProperty, ReferenceProperty,
-    STIXObjectProperty, IDProperty,
+    HashesProperty, IDProperty, ListProperty, ObservableProperty,
+    ReferenceProperty, STIXObjectProperty,
 )
 from stix2.v20.common import MarkingProperty
 
 from . import constants
 
-
 ID_PROP = IDProperty('my-type', spec_version="2.0")
 MY_ID = 'my-type--232c9d3f-49fc-4440-bb01-607f638778e7'
 
diff --git a/stix2/test/v21/test_custom.py b/stix2/test/v21/test_custom.py
index 1f86a27..e51d76a 100644
--- a/stix2/test/v21/test_custom.py
+++ b/stix2/test/v21/test_custom.py
@@ -1414,18 +1414,6 @@ def test_register_duplicate_observable_extension():
     assert "cannot be registered again" in str(excinfo.value)
 
 
-def test_register_duplicate_marking():
-    with pytest.raises(DuplicateRegistrationError) as excinfo:
-        @stix2.v21.CustomMarking(
-            'x-new-obj', [
-                ('property1', stix2.properties.StringProperty(required=True)),
-            ],
-        )
-        class NewObj2():
-            pass
-    assert "cannot be registered again" in str(excinfo.value)
-
-
 def test_allow_custom_propagation():
     obj_dict = {
         "type": "bundle",