Raise exception if undo is not implemented.

setup.cfg

@@ -105,7 +105,7 @@ addopts =
     --doctest-modules
 filterwarnings =
     ignore::DeprecationWarning
-
+    ignore::UserWarning
 
 [devpi:upload]
 # Options for the devpi: PyPI server and packaging tool

src/continuity/transforms/transform.py

@@ -32,17 +32,18 @@ def forward(self, tensor: torch.Tensor) -> torch.Tensor:
             Transformed tensor.
         """
 
-    @abstractmethod
     def undo(self, tensor: torch.Tensor) -> torch.Tensor:
-        """Undoes the inverse (given the transformation is bijective).
-
-        When the transformation is not bijective (one-to-one correspondence of data), the inverse/backward
-        transformation is not applied. Instead, a warning should be given to the user and an appropriate approximate
-        inverse transformation should be provided.
+        """Applies the inverse of the transformation (if it exists).
 
         Args:
             tensor: Transformed tensor.
 
         Returns:
-            Tensor with the transformation undone (given it is possible).
+            Tensor with the transformation undone.
+
+        Raises:
+            NotImplementedError: If the inverse of the transformation is not implemented.
         """
+        raise NotImplementedError(
+            "The undo method is not implemented for this transform."
+        )

tests/transforms/fixtures.py

@@ -1,6 +1,5 @@
 import pytest
 import torch
-import warnings
 
 from continuity.transforms import Transform
 
@@ -45,11 +44,7 @@ def forward(self, tensor: torch.Tensor) -> torch.Tensor:
             return torch.abs(tensor)
 
         def undo(self, tensor: torch.Tensor) -> torch.Tensor:
-            warnings.warn(
-                f"The {self.__class__.__name__} transformation is not bijective. "
-                f"Returns the identity instead!",
-                stacklevel=2,
-            )
+            """The `abs_transform` transformation is not bijective, therefore returns identity."""
             return tensor
 
     return Abs()

tests/transforms/test_transform.py

@@ -23,6 +23,4 @@ def test_transform_undo(plus_one_transform, random_tensor):
 
 
 def test_transform_undo_not_bijective(abs_transform, random_tensor):
-    with pytest.warns(UserWarning) as record:
-        assert torch.allclose(abs_transform.undo(random_tensor), random_tensor)
-    assert len(record) == 1
+    assert torch.allclose(abs_transform.undo(random_tensor), random_tensor)