fix(LoadImage): raise OptionalImportError when user-specified reader is not installed

monai/transforms/io/array.py

@@ -210,10 +210,10 @@ def __init__(
                     the_reader = look_up_option(_r.lower(), SUPPORTED_READERS)
                 try:
                     self.register(the_reader(*args, **kwargs))
-                except OptionalImportError:
-                    warnings.warn(
+                except OptionalImportError as e:
+                    raise OptionalImportError(
                         f"required package for reader {_r} is not installed, or the version doesn't match requirement."
-                    )
+                    ) from e
                 except TypeError:  # the reader doesn't have the corresponding args/kwargs
                     warnings.warn(f"{_r} is not supported with the given parameters {args} {kwargs}.")
                     self.register(the_reader())

tests/transforms/test_load_image.py

@@ -498,5 +498,18 @@ def test_correct(self, input_param, expected_shape, track_meta):
             self.assertFalse(hasattr(r, "affine"))
 
 
+class TestLoadImageReaderNotInstalled(unittest.TestCase):
+    def test_raises_when_user_specified_reader_not_installed(self):
+        """LoadImage must raise OptionalImportError when a user-specified reader's package is missing."""
+        from unittest.mock import patch
+
+        from monai.utils import OptionalImportError
+
+        # Patch ITKReader.__init__ to simulate the package not being installed
+        with patch("monai.data.image_reader.ITKReader.__init__", side_effect=OptionalImportError("itk not installed")):
+            with self.assertRaises(OptionalImportError):
+                LoadImage(reader="ITKReader")
+
+
 if __name__ == "__main__":
     unittest.main()