diff --git a/fastapi_crudrouter/core/_base.py b/fastapi_crudrouter/core/_base.py
index 376d54e..e45d33f 100644
--- a/fastapi_crudrouter/core/_base.py
+++ b/fastapi_crudrouter/core/_base.py
@@ -1,4 +1,4 @@
-from abc import abstractmethod
+from abc import ABC, abstractmethod
 from typing import Any, Callable, Generic, List, Optional, Type, Union
 
 from fastapi import APIRouter, HTTPException
@@ -10,7 +10,7 @@
 NOT_FOUND = HTTPException(404, "Item not found")
 
 
-class CRUDGenerator(Generic[T], APIRouter):
+class CRUDGenerator(Generic[T], APIRouter, ABC):
     schema: Type[T]
     create_schema: Type[T]
     update_schema: Type[T]
diff --git a/fastapi_crudrouter/core/_utils.py b/fastapi_crudrouter/core/_utils.py
index 118047b..ef3562e 100644
--- a/fastapi_crudrouter/core/_utils.py
+++ b/fastapi_crudrouter/core/_utils.py
@@ -33,7 +33,7 @@ def schema_factory(
     }
 
     name = schema_cls.__name__ + name
-    schema = create_model(__model_name=name, **fields)  # type: ignore
+    schema: Type[T] = create_model(__model_name=name, **fields)  # type: ignore
     return schema
 
 
diff --git a/tests/test_base.py b/tests/test_base.py
index ace1c40..399ec14 100644
--- a/tests/test_base.py
+++ b/tests/test_base.py
@@ -1,3 +1,6 @@
+from abc import ABC
+from typing import Type
+
 import pytest
 from fastapi import APIRouter, FastAPI
 
@@ -14,13 +17,30 @@
 from tests import Potato
 
 
-def test_router_type():
-    assert issubclass(CRUDGenerator, APIRouter)
-    assert issubclass(SQLAlchemyCRUDRouter, APIRouter)
-    assert issubclass(MemoryCRUDRouter, APIRouter)
-    assert issubclass(OrmarCRUDRouter, APIRouter)
-    assert issubclass(GinoCRUDRouter, APIRouter)
-    assert issubclass(DatabasesCRUDRouter, APIRouter)
+@pytest.fixture(
+    params=[
+        GinoCRUDRouter,
+        SQLAlchemyCRUDRouter,
+        MemoryCRUDRouter,
+        OrmarCRUDRouter,
+        GinoCRUDRouter,
+        DatabasesCRUDRouter,
+    ]
+)
+def subclass(request) -> Type[CRUDGenerator]:
+    return request.param
+
+
+def test_router_is_subclass_of_crud_generator(subclass):
+    assert issubclass(subclass, CRUDGenerator)
+
+
+def test_router_is_subclass_of_api_router(subclass):
+    assert issubclass(subclass, APIRouter)
+
+
+def test_base_class_is_abstract():
+    assert issubclass(CRUDGenerator, ABC)
 
 
 def test_raise_not_implemented():
@@ -35,9 +55,7 @@ def bar():
     methods = CRUDGenerator.get_routes()
 
     for m in methods:
-        with pytest.raises(NotImplementedError):
+        with pytest.raises(TypeError):
             app.include_router(CRUDGenerator(schema=Potato))
 
         setattr(CRUDGenerator, f"_{m}", foo)
-
-    app.include_router(CRUDGenerator(schema=Potato))