diff --git a/openedx_tagging/core/tagging/models/base.py b/openedx_tagging/core/tagging/models/base.py
index 6ec2e3cd..f8246308 100644
--- a/openedx_tagging/core/tagging/models/base.py
+++ b/openedx_tagging/core/tagging/models/base.py
@@ -244,7 +244,7 @@ def cast(self):
             )
 
         return self
-    
+
     def check_casted(self):
         """
         Double-check that this taxonomy has been cast() to a subclass if needed.
@@ -524,7 +524,7 @@ def value(self, value: str):
         Stores to the _value field.
         """
         self._value = value
-    
+
     @property
     def is_deleted(self) -> bool:
         """
diff --git a/openedx_tagging/core/tagging/models/system_defined.py b/openedx_tagging/core/tagging/models/system_defined.py
index c431e1c0..bcd90800 100644
--- a/openedx_tagging/core/tagging/models/system_defined.py
+++ b/openedx_tagging/core/tagging/models/system_defined.py
@@ -103,7 +103,7 @@ def tag_for_value(self, value: str):
         except ObjectDoesNotExist:
             raise Tag.DoesNotExist
         # Use the canonical value from here on (possibly with different case from the value given as a parameter)
-        value =  getattr(instance, self.tag_class_value_field)
+        value = getattr(instance, self.tag_class_value_field)
         # We assume the value may change but the external_id is immutable.
         # So look up keys using external_id. There may be a key with the same external_id but an out of date value.
         external_id = str(getattr(instance, self.tag_class_key_field))
diff --git a/tests/openedx_tagging/core/tagging/test_api.py b/tests/openedx_tagging/core/tagging/test_api.py
index 81c236a0..409e0933 100644
--- a/tests/openedx_tagging/core/tagging/test_api.py
+++ b/tests/openedx_tagging/core/tagging/test_api.py
@@ -257,9 +257,9 @@ def test_tag_object(self):
             # And the expected number of tags were returned
             assert len(object_tags) == len(tag_list)
             for index, object_tag in enumerate(object_tags):
-                assert object_tag.tag_id == tag_list[index].id
-                assert object_tag._value == tag_list[index].value
                 object_tag.full_clean()  # Should not raise any ValidationErrors
+                assert object_tag.tag_id == tag_list[index].id
+                assert object_tag._value == tag_list[index].value  # pylint: disable=protected-access
                 assert object_tag.taxonomy == self.taxonomy
                 assert object_tag.name == self.taxonomy.name
                 assert object_tag.object_id == "biology101"
@@ -277,7 +277,7 @@ def test_tag_object_free_text(self):
         object_tag.full_clean()  # Should not raise any ValidationErrors
         assert object_tag.taxonomy == self.taxonomy
         assert object_tag.name == self.taxonomy.name
-        assert object_tag._value == "Eukaryota Xenomorph"
+        assert object_tag._value == "Eukaryota Xenomorph"  # pylint: disable=protected-access
         assert object_tag.get_lineage() == ["Eukaryota Xenomorph"]
         assert object_tag.object_id == "biology101"
 
diff --git a/tests/openedx_tagging/core/tagging/test_models.py b/tests/openedx_tagging/core/tagging/test_models.py
index c7825190..d34299e3 100644
--- a/tests/openedx_tagging/core/tagging/test_models.py
+++ b/tests/openedx_tagging/core/tagging/test_models.py
@@ -444,7 +444,7 @@ def test_clean(self):
         with pytest.raises(ValidationError):
             object_tag.full_clean()
         object_tag.tag = self.tag
-        object_tag._value = self.tag.value
+        object_tag._value = self.tag.value  # pylint: disable=protected-access
         object_tag.full_clean()
 
     def test_tag_case(self) -> None:
@@ -476,7 +476,7 @@ def test_tag_case(self) -> None:
                 ).save()
 
     def test_is_deleted(self):
-        self.taxonomy.allow_multiple=True
+        self.taxonomy.allow_multiple = True
         self.taxonomy.save()
         open_taxonomy = Taxonomy.objects.create(name="Freetext Life", allow_free_text=True, allow_multiple=True)
 
diff --git a/tests/openedx_tagging/core/tagging/test_system_defined_models.py b/tests/openedx_tagging/core/tagging/test_system_defined_models.py
index 3026a844..c68144c4 100644
--- a/tests/openedx_tagging/core/tagging/test_system_defined_models.py
+++ b/tests/openedx_tagging/core/tagging/test_system_defined_models.py
@@ -34,21 +34,6 @@ class EmptyTestClass:
     """
 
 
-class InvalidModelTaxonomy(ModelSystemDefinedTaxonomy):
-    """
-    Model used for testing
-    """
-
-    @property
-    def object_tag_class(self):
-        return EmptyTestClass
-
-    class Meta:
-        proxy = True
-        managed = False
-        app_label = "oel_tagging"
-
-
 class TestLPTaxonomy(ModelSystemDefinedTaxonomy):
     """
     Model used for testing - points to LearningPackage instances
@@ -210,7 +195,7 @@ def test_tag_object_resync(self):
         api.tag_object(self.author_taxonomy, [self.user_1.username], object2_id)
         initial_object_tags = api.get_object_tags(object1_id)
         assert [t.value for t in initial_object_tags] == [self.user_1.username]
-        assert list(api.get_object_tags(other_obj_id)) == []
+        assert not list(api.get_object_tags(other_obj_id))
         # Change user_1's username:
         new_username = "new_username"
         self.user_1.username = new_username
@@ -222,7 +207,7 @@ def test_tag_object_resync(self):
         # This is good - all the objects throughout the system with this tag now show the new value.
         assert [t.value for t in api.get_object_tags(object2_id)] == [new_username]
         # And just to make sure there are no other random changes to other objects:
-        assert list(api.get_object_tags(other_obj_id)) == []
+        assert not list(api.get_object_tags(other_obj_id))
 
     def test_tag_object_delete_user(self):
         """