diff --git a/ppa/in_memory.py b/ppa/in_memory.py
index 540c373..8ea1ff1 100644
--- a/ppa/in_memory.py
+++ b/ppa/in_memory.py
@@ -1,43 +1,40 @@
+from collections.abc import Iterable
 from typing import Any, Type
 
 
 def in_memory_repository(
+    find_by_fields: Iterable[str] | None = None,
     entity_already_exists_exception: Type[Exception] = ValueError,
     entity_not_found_exception: Type[Exception] = ValueError,
 ):
+    if find_by_fields is None:
+        find_by_fields = []
     def decorator(cls) -> Type:
-        e_already_exists = entity_already_exists_exception
-        e_not_found = entity_not_found_exception
-
         class InMemoryRepository(cls):
-            find_by_fields: list[str] = ["id"]
-            entity_already_exists_exception: Type[Exception] = e_already_exists
-            entity_not_found_exception: Type[Exception] = e_not_found
-
             def __init__(self) -> None:
                 self._store: dict[str, Any] = {}
-                for key in self.find_by_fields:
+                for key in find_by_fields:
                     setattr(self, f"find_by_{key}", self._make_find_by_method(key))
 
             def add(self, entity: Any) -> Any:
                 if entity.id in self._store:
-                    raise self.entity_already_exists_exception()
+                    raise entity_already_exists_exception()
                 self._store[entity.id] = entity
 
             def retrieve(self, id_: Any) -> Any:
                 try:
                     return self._store[id_]
                 except KeyError as err:
-                    raise self.entity_not_found_exception() from err
+                    raise entity_not_found_exception() from err
 
             def update(self, entity: Any) -> None:
                 if entity.id not in self._store:
-                    raise self.entity_not_found_exception()
+                    raise entity_not_found_exception()
                 self._store[entity.id] = entity
 
             def delete(self, id_: Any) -> None:
                 if id_ not in self._store:
-                    raise self.entity_not_found_exception(id_)
+                    raise entity_not_found_exception()
                 del self._store[id_]
 
             def _make_find_by_method(self, field_name: str) -> Any:
diff --git a/ppa/test/test_in_memory.py b/ppa/test/test_in_memory.py
index 0cd4fce..d735cd5 100644
--- a/ppa/test/test_in_memory.py
+++ b/ppa/test/test_in_memory.py
@@ -3,36 +3,83 @@
 from ppa.in_memory import in_memory_repository
 
 
+class User:
+    def __init__(self, id_: int, name: str):
+        self.id = id_
+        self.name = name
 @pytest.fixture
-def User():
-    class User:
-        def __init__(self, id_: int, name: str):
-            self.id = id_
-            self.name = name
-
-    return User
+def user():
+    return User(1, 'john')
 
+@in_memory_repository(find_by_fields=[])
+class UserRepository:
+    pass
 
 @pytest.fixture
 def user_repository():
-    @in_memory_repository()
-    class UserRepository:
+    return UserRepository()
+
+
+def test_in_memory_repository_find_by_fields(user: User):
+    @in_memory_repository(find_by_fields=("id", "name"))
+    class FieldsRepository:
         pass
 
-    return UserRepository()
+    rep = FieldsRepository()
 
+    rep.add(user)
 
-def test_in_memory_repository(user_repository, User):
-    user = User(id_=1, name="John")
+    assert rep.find_by_id(user.id) == [user]
+    assert rep.find_by_name(user.name) == [user]
 
-    user_repository.add(user)
-    retrieved_user = user_repository.retrieve(1)
-    assert retrieved_user == user
+def test_in_memory_repository_exceptions(user: User):
+    class CustomException1(Exception):
+        pass
+
+    class CustomException2(Exception):
+        pass
+
+    @in_memory_repository(
+        entity_already_exists_exception=CustomException1,
+        entity_not_found_exception=CustomException2,
+    )
+    class ExceptionsRepository:
+        pass
+
+
+    rep = ExceptionsRepository()
 
-    updated_user = User(id_=1, name="Johny")
+    with pytest.raises(CustomException2):
+        rep.delete(user.id)
+
+    rep.add(user)
+    with pytest.raises(CustomException1):
+        rep.add(user)
+
+
+def test_in_memory_repository_methods(user_repository: UserRepository, user: User):
+    user_repository.add(user)
+    assert user_repository.retrieve(user.id) == user
+    updated_user = User(id_=user.id, name="john_updated")
     user_repository.update(updated_user)
-    assert user_repository.retrieve(1) == updated_user
+    modified_user = user_repository.retrieve(user.id)
+    assert modified_user.id == updated_user.id and modified_user.name == updated_user.name
+    user_repository.delete(user.id)
+    with pytest.raises(ValueError):
+        assert user_repository.retrieve(user.id)
+
 
-    user_repository.delete(1)
+def test_in_memory_repository_add_already_exists(user_repository: UserRepository, user: User):
+    user_repository.add(user)
     with pytest.raises(ValueError):
-        user_repository.retrieve(1)
+        user_repository.add(user)
+
+def test_in_memory_repository_update_not_found(user_repository: UserRepository, user: User):
+    with pytest.raises(ValueError):
+        user_repository.update(user)
+
+
+def test_in_memory_repository_delete_not_found(user_repository: UserRepository, user: User):
+    with pytest.raises(ValueError):
+        user_repository.delete(user)
+