From 62f866cb1dc405ddef0a29627dd1b3c267f28a29 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jon=20Haitz=20Legarreta=20Gorro=C3=B1o?=
 <jon.haitz.legarreta@gmail.com>
Date: Sun, 17 Aug 2025 22:18:16 -0400
Subject: [PATCH] REF: Inherit base model class from `ABC` to enforce native
 abstraction

Inherit base model class from `ABC` to enforce native abstraction.

Fixes:
```
Abstract methods are allowed in classes whose metaclass is 'ABCMeta'
```

raised locally by the IDE.
---
 src/nifreeze/model/base.py |  8 +++++---
 test/test_model.py         | 10 ++++++++++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/src/nifreeze/model/base.py b/src/nifreeze/model/base.py
index d4f944bc..540ee812 100644
--- a/src/nifreeze/model/base.py
+++ b/src/nifreeze/model/base.py
@@ -22,7 +22,7 @@
 #
 """Base infrastructure for nifreeze's models."""
 
-from abc import abstractmethod
+from abc import ABC, ABCMeta, abstractmethod
 from typing import Union
 from warnings import warn
 
@@ -77,7 +77,7 @@ def init(model: str | None = None, **kwargs):
         raise NotImplementedError(f"Unsupported model <{model}>.")
 
 
-class BaseModel:
+class BaseModel(ABC):
     """
     Defines the interface and default methods.
 
@@ -88,6 +88,8 @@ class BaseModel:
 
     """
 
+    __metaclass__ = ABCMeta
+
     __slots__ = ("_dataset", "_locked_fit")
 
     def __init__(self, dataset, **kwargs):
@@ -116,7 +118,7 @@ def fit_predict(self, index: int | None = None, **kwargs) -> Union[np.ndarray, N
             If ``None``, no prediction will be executed.
 
         """
-        raise NotImplementedError("Cannot call fit_predict() on a BaseModel instance.")
+        return None
 
 
 class TrivialModel(BaseModel):
diff --git a/test/test_model.py b/test/test_model.py
index a4545860..b4c0924f 100644
--- a/test/test_model.py
+++ b/test/test_model.py
@@ -35,6 +35,16 @@
 from nifreeze.testing import simulations as _sim
 
 
+def test_base_model():
+    from nifreeze.model.base import BaseModel
+
+    with pytest.raises(
+        TypeError,
+        match="Can't instantiate abstract class BaseModel without an implementation for abstract method 'fit_predict'",
+    ):
+        BaseModel(None)
+
+
 @pytest.mark.parametrize("use_mask", (False, True))
 def test_trivial_model(request, use_mask):
     """Check the implementation of the trivial B0 model."""